US A1 (19) United States (12) Patent Application Publication (10) Pub. N0.: US 2011/ A1 Sheer (43) Pub. Date: Aug.

Transcription

1 US A1 (19) United States (12) Patent Appication Pubication (10) Pub. N0.: US 2011/ A1 Sheer (43) Pub. Date: Aug. 11, 2011 (54) SOCKET SMTP LOAD BALANCING (52) US. C /206; 709/226; 726/9 (57) ABSTRACT (75) Inventor: Pau sheer Amsterdam (NL) A method is provided for oad baancing SMTP, POP, and IMAP traf?c over a puraity of backend SMTP, POP, and (73) ASSigneeI P3111 Sheer, Amsterdam (NL) IMAP s for sites that host a arge number of eectronic mai accounts. The method aows the tota set of hosted mai (21). App' NO" 12/702,584 accounts to be divided into subsets, Where each subset is handed by one or more backend s. The method ensures _ that each SMTP, POP, or IMAP connection is directed to a (22) Fedi Feb- 9, 2010 backend that handes the subset to Which the recipient Pubication Cassi?cation emai address associated With the connection is assigned. This method incudes agorithms to interpret incoming SMTP, POP and IMAP connections in such a Way as to (51) IIt- C- identify the recipient(s) and estabish corresponding connec G06F 15/16 ( ) tions to backend (s) Whie giving the appearance (to the H04L 29/06 ( ) connecting party) of connecting directy to a backend. Exampe SMTP depoyment. An organization hosts mai for the Mai deivery with recipient address adam@0rg. us though- _ zach@0rg. us outside emai R10s Internet k) emai emai emai se rver emai se rver udum@org. us through harry@ org. us henry@org. us through marge@org. us mury@ org. us through rob@org. us roger@org. us through zach@org. us

2 Patent Appication Pubication Aug. 11, 2011 Sheet 1 0f 6 US 2011/ A1 FIG. 1. Exampe SMTP depoyment. An organization hosts mai for the Mai deivery with recipient address adam@org.us though zach@org.us _ outside emai Server Internet I oad baancer 'L S r/ 2\ I emai emai emai emai I g é I adam@org. us henry@org. us mary@ org. us roger@org. us through through through through harry@org. us marge@org. us us zach@org. us

3 Patent Appication Pubication Aug. 11, 2011 Sheet 2 0f 6 US 2011/ A1 FIG. 2. Exampe POP/IMAP depoyment. An organization hosts mai for the recipient address \ adam@org.us though us 07 Internet Organization LAN 103 i 0 oad baancer f 6 L. adam@org. us henry@org. us mary@ org. us roger@org. us through through th rough harry@0rg. us marge@0rg. us us us

4 Patent Appication Pubication Aug. 11, 2011 Sheet 3 0f6 US 2011/ A1 FIG. 3. Steps for deivery using SMTP: EHLO" through "RCPT". Sequence diagram showing a singe end-to-end deivery of an emai. outsde emai oad baancer_,/\106.. emai Server. ema connect in f EHLO Ok MAIL 250 Ok RCPT TO:<adam@org.us> foz connect 220 in MAIL FROM:<seth RCPT TO:<adam or.us> 250 0k 303 RCPT TO:<henry@org.us> / /. connect ( 220 Info EH L0 250 Ok 1 MAIL FROM:<seth@q.com> ( 250 Ok RCPT TO:<henry@org.us> 250 0k 250 ok ( -

5 Patent Appication Pubication Aug. 11, 2011 Sheet 4 0f 6 US 2011/ A1 FIG. 4. Steps for deivery using SMTP: DATA" through "QUIT". Sequence diagram showing a singe end-to-end deivery of an emai. outside emai 106 emai 108 Server oad baancerf f emai W 354 continue emai data chunk 1 emai data chunk 1 emai data chunk 1 emai data chunk 2 $406 emai data chunk 2 emai data chunk 2 As many chunks up to the fu ength of the emai data emai data chunk n emai data chunk n emai data chunk n Command interactions beyond this point do not improve carity of the exampe of the method to those skied in the art

6 Patent Appication Pubication Aug. 11, 2011 Sheet 5 0f 6 US 2011/ A1 FIG. 5. Steps for retrieva using POP/ IMAP. Sequence diagram showing end-to-end retrieve of emai. Steps shown, individua commands omitted for carity. 209 POP/IMAP cient-f- oad baanceuf 106 femai connect and greet authenticate authentication success connect and greet authenticate f5 05 authentication success transparent forwarding transparent forwarding

7 Patent Appication Pubication Aug. 11, 2011 Sheet 6 0f 6 US 2011/ A1 FIG. 6. Steps for sending by reay using SMTP. Sequence diagram showing end-to-end sending of emai. Steps shown, individua commands omitted for carity. 106 outside emai SIVITP cient oad baancerf connect and greet authenticate authentication success connect and greet tronsparentforwording transparent forwarding

8 US 2011/ A1 Aug. 11,2011 SOCKET SMTP LOAD BALANCING BACKGROUND OF THE INVENTION [0001] 1. The Fied of the Invention [0002] The present invention reates to means or steps for apportioning resources to one or more computers on a net Work. More speci?cay, the present invention reates to sys tems and methods used to distribute emai (eectronic mai) deivery and retrieva over a number of emai s in order to reduce the oad of tra?ic to/ from individua emai s, and/or systems and methods to scae emai hosting environ ments to hande arger amounts of emai and arger numbers of mai boxes With ower resource consumption and/or ower atency and/ or higher throughput. [0003] 2. The Prior State oftheart [0004] An organization that depoys an emai soution Wi usuay support at east one or more of the foowing services: a system to receive incoming emai deiveries from an outside emai and store them for retrieva; a system to aow retrieva from storage; and a system to reay outgoing emai on behaf of senders. The storage pertaining to an individua recipient is caed a mai box. [0005] The Internet standard protoco for deivering emai is caed the Simpe Mai Transfer Protoco (SMTP) primariy de?ned in IETF document RFC The Internet standard protoco by Which recipients usuay retrieve emai from stor age is the Post O?ice Protoco (POP) and/ or the Internet Message Access Protoco (IMAP) primariy de?ned in IETF documents RFC 1939 and RFC 3501 respectivey. Both these protocos are usuay impemented by a singe commodity computer such that a emai is received by that emai, stored Within that one emai s storage media, and retrieved from the same emai by the recipient. In many cases, that emai may have redundant repication of the storage and/ or standby emai s to mitigate a faiure of the emai. [0006] A arge organization Wi typicay be required to diverge from the herein described singe commodity com puter system When they reach upwards of 1,000, 10,000, or 100,000 mai boxes due to unfavorabe atency and throughput, and/or poor stabiity. [0007] To introduce improved scaabiity to the depoyment scenario of a singe commodity computer system, a common method is to depoy a puraity of emai s using DNS (Domain Name System) oad baancing to share the oad of incoming emai. This is impemented by advertis ing more than one DNS resource record for the provided mai service. An outside SMTP cient trying to initiate an SMTP deivery to the service Wi thereby pick one emai from among the puraity of emai s. These mutipe emai s Woud then share the same contiguous singe storage device (such as an NFS?e-system,?ber channe SAN, or other shared?e-system). The subsequent operation of using POP/IMAP to retrieve emai, ikewise chooses from one or more emai s that have access to the same shared stor age device. A variation of such a system is US. Pat. No. 9,746,952 (Fodor). This depoyment scenario has the disad vantage that the throughput of the system as a Whoe is greaty dependent on the throughput of the shared storage device, Which may suffer from a many-to-many thrashing effect, network bandwidth imits, or other genera throughput de? ciencies. These probems are exacerbated by adding more emai s. A further probem occurs in the common case of attempting to impement a spam-?tering or virus-?tering method on the emai : mutipe s may be required to share data, incurring further computation overhead. [0008] Another method to achieve scaabiity is to divide the set of emai addresses into sub-domains. For instance, rather than hosting a arge number of emais adam@org.us through Zach@org.us (a With the same domainportion of the emai instead, the organization coud name emais by department, such as adam@ny.org.us, henry@ca.org.us, Zach@nc.org.us, etc. Emai s can thereby be depoyed such that each emai hosts a subset of emais of one department. This method compromises on?exibiity, and requires migration. This method does not Work for an organization such as an ISP (Internet Service Provider) that Wishes to use the same domain for a subscriber emai accounts. [0009] The state of the art aso incudes various combina tions of depoyment scenarios. Some of these depoyment scenarios make use of the method of forwarding emai between emai s. The method of forwarding emai fo ows the steps of accepting deivery of the emai and storing the entirety of the emai Within storage media (voatie or otherwise), and then retrieving the emai from the storage media, and then deivering the emai to another, in a manner such as to apportion Workoad. The intermediate step of storing the entirety of the emai incurs the disadvantage of consuming substantia computing resources. Systems that incude Within their methods such forwarding are US. Pat. No. 7,272,662 (Chesnais) and US. patent appication Ser. No. 10,278,824 (Fenton). These systems do not attempt to address the herein described disadvantage, nor do they sove the probem of interpreting the SMTP session in such a Way as to redirect the session based on the recipient emai address. [0010] In terms of generic oad baancing of cient connec tions, there are a number of popuar methods. These methods are mosty empoyed for Web traf?c, that is, the HTTP pro toco, but can aso be appied to SMTP, POP, and IMAP. Generic oad baancing intercepts the data from the cient and directs it to a machine from among the puraity of machines sharing oad. See for exampe US. Pat. No. 6,473, 802 (Masters), US. Pat. No. 6,182,139 (Brende), US. Pat. No. 6,128,279 (O Nei), oru.s. Pat. No. 6,772,211 (Lu). The oad baancer may interpret and/ or modify the data in passing. In particuar, some oad baancers interpret the initia portion of the data of a new connection and direct the connection to a machine of choice. For exampe, for the HTTP protoco, the oad baancer Woud intercept the cookie header Which may contain information indicating to Which machine the connec tion shoud be directed. HoWever the state of the art does not incude oad baancers that are abe to adequatey interpret emai handing protocos in order to choose the backend machine in a manner that aows subdivision of mai boxes into smaer sets; nor do so such that each oad sharing machine handes ony a smaer set of mai boxes. This sub division in conjunction With session redirection is a principe advantage of the present invention. SUMMARY AND OBJECTS OF THE INVENTION [0011] The probems in the prior state of the art have been successfuy overcome by the present invention Which is directed to systems and methods for oad baancing SMTP, POP and IMAP sessions over a puraity of emai s such that a POP/IMAP retrieva session pertaining to a recipient Wi be directed to the same to Which an SMTP deivery

9 US 2011/ A1 Aug. 11,2011 operation from an outside emai Was previousy directed for the same recipient. [0012] The present invention utiizes methods for deiver ing and retrieving emai de?ned in RFC 5321, RFC 1939 and RFC 3501, incorporated herein by reference. [0013] The present invention utiizes the method that a puraity of emai s are depoyed, and that each emai has a distinguishing designator, and that each emai address has assigned to it at east one of these designators, and that such assignments are stored in a database, and that each emai be ready to accept emai for those emai addresses assigned With its designator. [0014] The emai database may aso store aias emai address information necessary for performing emai address substitutions and ist expansions as may be required by the recipients communication needs. The manner of aias emai addresses is We known to those skied in the art. [0015] The emai database may aso store secret passwords and identifying tokens required for authentication, such that there is a mapping between recipient emai addresses and identifying tokens. It may store a secret password for each identifying token. [0016] An emai deivery operation may begin With an out side emai initiating a connection to the organization s ho sting SMTP. By the methods of the present invention this SMTP may be substituted by the herein described oad baancer. The oad baancer performs the methods of SMTP handshaking as de?ned by RFC 5321 up to the point of receiving the SMTP command RCPT. Before repying to RCPT, the oad baancer may extract the recipient emai address from the RCPT ine of command, and perform a ook-up from the emai database, to determine if the recipient emai address is indeed an emai address for Which the orga nization hosts emai (i.e. a oca emai address), as We as retrieve the designator(s) With Which it has been assigned, as We as perform any ist expansions or address substitutions, as We as ook up their respective designators, in a recursive fashion, etc. [0017] The oad baancer may then resove a designators to their actua emai identi?ers and attempt to make a connection to each reevant emai. The oad baancer may then perform the methods of SMTP handshaking as de?ned by RFC 5321 mimicking the same MAIL ine of command, and issuing a necessary RCPT commands If a RCPT commands to a emai s resut in successfu SMTP repy codes then the oad baancer may repy With a successfu SMTP repy code to the outside emai. If a singe RCPT command to an emai does not resut in a successfu SMTP repy code then the oad baancer may repy With a faied SMTP repy code to the outside emai. [0018] The outside emai Wi possiby send more RCPT commands Which may be handed in the same Way, preferaby reusing connections to emai s. [0019] Those skied in the art Wi be aware that most emai deiveries are to a singe recipient and therefore the oad baancer is ikey to require a connection to ony one emai for an individua emai deivery. [0020] The outside emai may send a DATA com mand, and the oad baancer my mimic a DATA command to each of the emai s to Which it is connected. Once again, if any one emai returns a faiure SMTP repy code, the oad baancer may return a faiure SMTP repy code to the outside emai. [0021] The outside emai may begin to send the emai. The oad baancer may receive the emai in chunks reated to the TCP packetization of the data stream. After receiving a chunk, the oad baancer may Write the chunk in fu to each of the emai s to Which it is connected before proceeding to receive the next chunk. If any singe chunk fais to Write in fu to an emai then that emai transaction may be considered to have faied and an appropriate faiure repy code may be returned to the outside emai. [0022] Each emai may respond With a repy code. If a such repy codes indicate successfu deivery, a success repy code may be returned to the outside emai. The possibiity exists that not a emai s give the same repy, meaning that one or more s have accepted the emai Whereas one or more other s have rejected the emai. In this case the faiure repy code may be of the form indicating that the outside emai shoud not attempt a sub sequent deivery for the same emai. (If the oad baancer imposes a size imit on the emai data, and that imit is smaer than that of any of the emai s, then the herein described scenario of differenty repying emai s is unikey to occur. That this unexpected outcome is empiricay true is one of the reasons that the present invention is non-obvious.) [0023] If required, the outside emai may continue an additiona MAIL command, thus repeating the preceding steps. [0024] In this Way, the outside emai is given the appearance of performing SMTP command interactions directy With the emai. The emai is given the appearance of performing SMTP command interactions With an outside emai. Both are given the appearance of a suf?cienty standards-compiant SMTP session according to the methods of the SMTP standard RFC 5321 (or other ver sions of the standard). [0025] An advantage of the present invention is that the compete emai data are not stored on the oad baancer, the storage of Which Woud impart additiona computationa bur den on the oad baancer. Such resources incude consump tion of persistent or voatie storage media, and/ or consump tion of rate of transfer or bandwidth to or from persistent or voatie storage media. [0026] By the methods of the present invention, deivery faiures due to unavaiabiity of an emai, or faiures due to poicy reasons, or faiures due to the recipient address being invaid, or faiures due to other reasons, are reported to the outside emai eary in the session; the onus being on the outside emai to retry or fai deivery if required by the SMTP protoco. This has the advantage of saving on network bandwidth by preventing the session from reaching the DATA command, and by obviating the need for bounce messages. State of the art emai forwarding techniques queue a incoming emai, Which typicay contains a arge portion (sometimes 90% in practice) of undeiverabe emai mes sages, Which therefore bounces and consumes computing resources. [0027] The connection to the emai is described herein as taking pace at the point in the sequence of com mands directy after the arriva of the RCPT command from the outside emai. HoWever, those skied in the art Wi reaize that some variation in the sequences of operation is viabe and Wi have the same resut. The exampe herein shoud not be construed to imit the scope of the invention. [0028] By the methods of the present invention emai Wi have been deivered to a backend of the organizations

10 US 2011/ A1 Aug. 11,2011 choosing without incurring any intermediate queuing, stor age or processing. The deivery is transparent to both the emai and the outside emai. This has the desir abe property that the emai s can continue to use or icense whichever SMTP software/hardware impementation the organization has previousy depoyed. [0029] Further, spam?tering methods (such as Grey-List ing or Sender Poicy Framework) can be impemented on the oad baancer (at the point of receiving the MAIL and/or RCPT commands), with the advantage of a singe Grey Listing database, and the further advantage of protection of emai s from unwanted connections and denia-of-ser vice attacks. Spam detection methods that require arge amounts of computations (due to their in-depth anaysis of emai content) can take pace on the emai s, with the advantage of apportioning the computationa oad. [0030] For the retrieva of emai by recipients, POP/IMAP cients may connect to the oad baancer. The POP/IMAP cient may try to authenticate itsef to the oad baancer using one of the authentication methods commony used for POP/ IMAP and known to those skied in the art. The process of authentication may necessitate that an identifying token?rst be sent to the oad baancer. The oad baancer may then retrieve from the emai database to obtain the recipient emai address mapped to that identifying token and subsequenty to obtain designator(s) to which the emai address has been assigned. [0031] The oad baancer may then resove a designators to their actua emai identi?ers and attempt to make a connection to each reevant emai as though the oad baancer were a POP/IMAP cient. The next step of the authentication may invove cryptographic operations and/or the exchange of secret passwords. The oad baancer may pass these secret passwords between the POP/IMAP cient and the emai. In the case of authentication methods that invove cryptography such that the secret password cannot be extracted, the oad baancer may retrieve the secret password from the emai database, and make use of that secret password to authenticate the POP/IMAP cient as we as to authenti cate itsef to the emai. [0032] The identifying token may be identica to the recipi ent emai address thus making trivia the mapping between the identifying token and the recipient emai address. [0033] Subsequent to the herein described connection and authentication steps, the oad baancer may transparenty for ward data between the POP/IMAP cient and the emai. According to the methods of the present invention the oad baancer woud have the appearance to the POP/IMAP cient of communicating directy with the emai. [0034] For the reaying (i.e. sending) of emai by senders, SMTP cients may connect to the oad baancer. The SMTP cient may try to authenticate itsef simiar to the authentica tion of POP/ IMAP cients herein described. Subsequent to the connection and authentication steps, the oad baancer may transparenty forward data between the SMTP cient and the emai. According to the methods of the present inven tion the oad baancer woud have the appearance to the SMTP cient of communicating directy with the emai. The emai may then proceed to queue the emai for outgoing deivery. [0035] The advantage of using the oad baancer for send ing emai as herein described is so that white ists or associa tions between senders (reverse path emai addresses) and recipients can be gathered or stored by the oad baancer and assist in spam?tering. Systems and methods for empoying such white ists or associations in spam?ters are we known to those skied in the art. [0036] A further advantage of the present invention is with regard to emai interception and repication. Certain jurisdic tions require that emai systems have the capabiity to inter cept and archive emai so that in the event of a ega court order to perform interception or archiva for particuar recipi ents, those emai systems are abe to do so forthwith. The addition of an address expansion or aias in the emai database woud resut in an additiona emai deivery, potentiay to a dedicated emai, which woud serve this purpose. Fur ther, and in genera, because a emai passes through the oad baancer, interception of emai is simpi?ed. The present invention therefore has the advantage that it simpi?es an organizations methods to compy with oca aw pertaining to emai interception and/or archiva. BRIEF DESCRIPTION OF THE DRAWINGS [0037] In order that the manner in which the above-recited and other advantages and objects of the invention are obtained, a more particuar description of the invention brie?y described above wi be rendered by reference to spe ci?c embodiments thereof which are iustrated in the appending drawings. Understanding that these drawings depict ony typica embodiments of the invention and are not therefore to be considered imiting of its scope, the invention wi be described and expained with additiona speci?city and detai through the use of the accompanying drawings in which: [0038] FIG. 1 is an exampe of a suitabe depoyment of the present invention showing connections between components of the system for an SMTP deivery. [0039] FIG. 2 is an exampe of a suitabe depoyment of the present invention showing connections between components of the system for POP/IMAP retrieva. [0040] FIG. 3 is an exampe of a sequence diagram of seected SMTP commands of the SMTP protoco, by the methods of the present invention, for the deivery of emai from an outside emai to an emai. [0041] FIG. 4 is an exampe ofthe same as FIG. 3 wherein further seected commands are shown. [0042] FIG. 5 is an exampe of a sequence diagram of seected POP/IMAP steps of interaction, by the methods of the present invention, for the retrieva of emai by a POP/ IMAP cient. [0043] FIG. 6 is an exampe of a sequence diagram of seected SMTP steps of interaction, by the methods of the present invention, for the reaying of emai by an SMTP cient. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0044] The invention is described beow by using diagrams to iustrate the processing of embodiments used to impe ment the systems and methods of the present invention. Using the diagrams in this manner to present the invention shoud not be construed as imiting its scope. [0045] The present invention contempates both methods and systems for the oad baancing of emai retrieva and deivery. The embodiments of the present invention may com prise a specia purpose or genera purpose computer compris ing various computer hardware as discussed beow.

11 US 2011/ A1 Aug. 11,2011 [0046] Embodiments Within the scope of the present inven tion aso incude computer systems 101 having persistent storage media 1 02, voatie storage media, executabe instruc tions, and network communication inks. By Way of exampe and not imitation, such computing systems may be a genera purpose microprocessor-based computer With a hard-disk or soid-state-disk storage media, a Loca Area Network 104 (LAN) or Wide Area Network (WAN) network communica tion device, and there may be a puraity of these computing systems depoyed to aow network communications between them. [0047] The computer systems may impement the network communication protocos of the Internet Protoco (IP) and of the Transmission Contro Protoco (TCP), and may be abe to operate as a node Within the Internet and/or a LAN. The computer systems may impement communication between one another using connections based on TCP and accept incoming connections or initiate outgoing connections. The computing systems may be instaed With genera-purpose operating systems such as Microsoft WindoWs, or operating systems conforming to the POSIX standard, or Unix-ike operating systems, or other genera purpose operating sys tems, or embedded or specia-purpose operating systems. The computer systems may have genera purpose functions for mapping data items to data keys in the manner of a database and persistenty storing these mappings as We as aowing insertions, updates and deetions of mappings. [0048] The emai s 105 may contain executabe instructions that impement the protocos of SMTP, POP or IMAP. By Way of exampe and not imitation, these execut abe instructions may be in the form of genera-purpose emai handing software. [0049] The emai handing software may have a oca per sistent store of a set of recipient emai addresses for Which the computer system is prepared to accept incoming mai mes sages by Way of the SMTP protoco, as We as a maibox store for each recipient to hod deivered mai messages. The emai handing software may be prepared to aow retrieva of mai messages from the maibox store by outside computer sys tems using the POP or IMAP protocos. The emai handing software may impement an authentication mechanism to vaidate the authenticity of incoming POP or IMAP connec tions. The authentication mechanism may aow ony outside computer systems that are in possession of per-recipient secret information, such as a password or key, to aow retrieva of mai. [0050] Each backend s set of recipient emai addresses may be a subset of the tota of a recipient emai addresses hosted by the embodiment. The backend s set of recipient emai addresses may overap that of another backend. [0051] At east one of the computer systems, the oad ba ancer 1 06, sha impement the method of accepting incoming connections from outside emai s 108 and outside POP/ IMAP cients 209, and making connections 103 to emai s. SMTP, IMAP, and POP commands and repies may be passed aong a session 107 between the outside cients/ s and the oad baancer. SMTP, IMAP and POP com mands may be passed between the oad baancer and the backend s. The oad baancer may hod connections open to the outside cients/s Whie at the same time hoding a connection open to the backend s, and may reay commands and repies between the backend s and the outside cients/s. The reay of commands and repies may invove dupication or ateration. [0052] The oad baancer may have access to an emai data base. In the preferred embodiment of the invention the emai database may be stored Within the oad baancer on a persis tent storage media and/ or in a voatie storage media, the atter possiby for reasons of performance. The database may aso be stored remotey and be accessibe to the oad baancer in such a manner as is famiiar to those skied in the art. By Way of exampe and not imitation, in the preferred embodiment of the invention, the oad baancer may have an in-memory hash-tabe of a hosted emai addresses and identifying tokens, associated to any data that may be required as herein described in terms of database and ook up. [0053] The DNS service pertaining to the domain part of a emai addresses in the herein described database may be con?gured With MX (Mai Exchanger) records pointing to the oad baancer. [0054] By Way of exampe and not imitation, the preferred embodiment herein described may incude a connection-ori ented software impementation Which can accept incoming connections and initiate outgoing connections. The connec tions may, by Way of exampe, be TCP/IP connections, and may be accessibe through an Appication Programming Interface (API), Which may be the Berkeey Socket API, the WindoWs Socket API, or other API. The connections require handing in a concurrent fashion so that a puraity of sessions of emai retrieva and/or deivery are handed concurrenty; such being famiiar to those skied in the art. Such concurrent handing may be impemented using a muti-threaded pro gramming mode, an event-based state-machine program ming mode, a cooperative threading programming mode, or other programming mode, or a programming mode that is a combination of one or more of those herein described. Because some programming modes may be better suited to hande very arge numbers of concurrent connections, the programming mode may be thusy chosen, however the invention is not imited to a speci?c programming mode. [0055] In the preferred embodiment of the invention the oad baancer may send commands, by Way of exampe, according to the sequence shown in FIG. 3 and FIG. 4. [0056] The oad baancer may interact With the outside emai according to part of the interactions 301 of the SMTP protoco. Herein the terms 220, EHLO, 250, MAIL FROM, and RCPT TO are famiiar to those skied in the art. [0057] The oad baancer may ook up 302 from the data base, the emai designator corresponding to the recipi ent emai, and any aias expansions and associated emai addresses as We as their respective emai designators, in a recursive fashion. The oad baancer Wi then connect 303 to the emai corresponding to the designator. [0058] The oad baancer may interact With the emai according to the interactions 304 of the SMTP protoco. Herein the terms 220, EHLO, 250, MAIL FROM, and RCPT TO are famiiar to those skied in the art. If a faiure repy code is returned by the emai, then the same faiure repy code may be returned by the oad baancer to the outside emai. There is one case, however, Where the same repy code may not be sent: if an error repy code is returned by the emai in response to a RCPT TO Where the same emai has previousy returned a suc cess repy code in response to a prior RCPT TO. For this

12 US 2011/ A1 Aug. 11,2011 exception a 5yZ response code may be substituted in order to prevent dupicate deiveries. [0059] The oad baancer may interact With the outside emai according to the remainder of the interactions 405 of the SMTP protoco. Herein the terms DATA and 354 are famiiar to those skied in the art. In order to ensure that a emai s receive the compete emai data, the oad baancer may perform the interactions 406 of fuy transmit ting each chunk to a emai s before proceeding to receive the next chunk. The?rst chunk may be prepended With a Receivedz header for compiance With the SMTP protoco. [0060] The steps herein may be repeated as required by the outside emai. [0061] In the preferred embodiment of the invention the oad baancer may additionay send groups commands, by Way of exampe, according to the sequence shown in FIG. 5. [0062] The POP/IMAP cient may connect 501 and authen ticate 502 itsef to the oad baancer using one of the methods of authentication We known to those skied in the art. This incudes, by Way of exampe, the authentication methods of APOP, LOGIN, NTLM, or CRAM-MDS. [0063] The oad baancer may ook up 503 from the data base, the emai designator corresponding to the iden tifying token of the authentication step, and then connect 504 to the corresponding. In the preferred embodiment of the invention the identifying token is mapped to the recipi ent s emai address or is identica to the recipient s emai address. [0064] The oad baancer may interact 505 With the emai according to the interactions of the POP/IMAP proto co. [0065] In the preferred embodiment of the invention the oad baancer may additionay send groups commands, by Way of exampe, according to the sequence shown in FIG. 6. [0066] The SMTP cient may connect 601 and authenticate 602 itsef to the oad baancer using one of the methods of authentication We known to those skied in the art. This incudes, by Way of exampe, the authentication methods of PLAIN, LOGIN, NTLM, or CRAM-MDS. [0067] The oad baancer may ook up 603 from the data base, the emai designator corresponding to the iden tifying token of the authentication, and then connect 604 to the corresponding. In the preferred embodiment of the invention the identifying token is mapped to the sender s emai address (reverse path emai address) or is identica to the sender s emai address. [0068] The oad baancer may transparenty forward 605 data between the SMTP cient and the emai. [0069] The preferred embodiment herein described, refers to the SMTP cient as authenticating itsef using an authenti cation method that empoys an identifying token. Such authentication may be dispensed With if the IP address of the SMTP cient is Within the ream of IP addresses aowed to reay mai. In this case, instead of an identifying token, the sender emai address (reverse path emai address) may be used to ook up the emai designator from the database. The remainder of the interactions proceed simiary forth With. [0070] The preferred embodiment herein described refers to SMTP but shoud not be construed as imiting the scope of the invention to this protoco ony. Other protocos that enabe the deivery of emai, as We as protocos based on SMTP, or protocos that are re?nements or extensions to SMTP are aso incuded Within the scope of the invention. [0071] The preferred embodiment herein described refers to POP/IMAP but shoud not be construed as imiting the scope of the invention to these two protocos ony. Other protocos that enabe the retrieva of emai, as We as proto cos based on POP or IMAP, or protocos that are re?nements or extensions to POP or IMAP are aso incuded Within the scope of the invention. [0072] The preferred embodiment may incude a puraity of computer systems each a oad baancer. A oad baancers may be isted as DNS MX records for a reevant domains. Outside SMTP connections may then choose a oad baancer from the set of reevant MX records in such a Way as to avoid those that are unavaiabe due to faiure. This embodies a mutipy redundant service, toerant to faiures of individua oad baancer computer systems. Both embodiments empoy ing a singe oad baancer as We as embodiments empoying a puraity of oad baancers, are incuded Within the scope of the present invention. What is caimed is: 1. A system for distributing emai deiveries over a puraity of emai s comprising the steps of: intercepting the emai deivery session; identifying emai recipients Within the emai deivery ses sion; resoving emai recipients to corresponding emai s that are prepared to accept deivery for those recipients; and repicating, possiby With modi?cation, the emai deivery session toward the corresponding emai s; Wherein the emai deivery sessions are processed in an over apping fashion such that ony discrete parts of the emai message data are at any one time stored or known to the intercepting component of the system. 2. The method of caim 1, further comprising the step of expanding identi?ed emai recipients into a puraity of aias emai recipients, Wherein the system then proceeds according to the steps for each. 3. A system for distributing emai retrievas over a puraity of emai s comprising the steps of: intercepting the authentication step of the emai retrieva session; identifying the emai recipient from the authentication tokens; resoving the emai recipient to a corresponding emai that is prepared to accept retrieva by that recipi ent; and repicating, possiby With modi?cation, the emai retrieva session toward the corresponding emai ; Wherein the emai retrieva sessions are processed in an over apping fashion such that ony discrete parts of the emai message data are at any one time stored or known to the intercepting component of the system. 4. The method of caim 3 further comprising the imitation that, for each recipient, the emai retrieva session is repi cated to the same emai as Woud an emai deivery session for the same recipient. 5. A system for distributing emai deiveries for authorized senders over a puraity of emai s comprising the steps of:

13 US 2011/ A1 Aug. 11,2011 intercepting the emai deivery session; identifying the emai sender Within the emai deivery ses sion; resoving the emai sender to a corresponding emai that is prepared to reay the deivery for that sender; and repicating, possiby With modi?cation, the emai deivery session toward the corresponding emai ; Wherein the emai deivery sessions are processed in an over apping fashion such that ony discrete parts of the emai message data are at any one time stored or known to the intercepting component of the system. 6. The method of caim 5 further comprising the imitation that, for an emai sender, the emai deivery session is repi cated to the same emai as Woud the emai deivery session of the same emai recipient. * * * * *