TCP/IP SMTP User Exits Support APAR PQ14324 VM TCP/IP ... - IBM

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ContentsBackground . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1The SMTP Envelope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1General Exit Information . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3Client Verification Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Mail Forwarding Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4SMTP Commands Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5SourceRoutes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5Client Verification Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7Built-in Client Verification Function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7VERIFYCLIENT Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8SMSG SMTP VERIFYCLIENT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9Client Verification Exit Parameter Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10REXX Parameter List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12ASSEMBLER Parameter List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Parameter Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13Client Verification Exit Return Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14Client Verification Sample Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15Mail Forwarding Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16FORWARDMAIL Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16SMSG SMTP FORWARDMAIL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18Mail Forwarding Exit Parameter Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19REXX Parameter List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20ASSEMBLER Parameter List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Parameter Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21Mail Forwarding Exit Return Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23Mail Forwarding Sample Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24SMTP Commands Exit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25SMTPCMDS Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26SMSG SMTP SMTPCMDS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28SMTP Commands Exit Parameter Lists . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30REXX Parameter List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Inputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31Outputs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31ASSEMBLER Parameter List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Parameter Descriptions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32SMTP Commands Exit Return Codes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34Sample SMTP Commands Exits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35Source Routes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36SOURCEROUTES Statement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36SMSG SMTP SOURCEROUTES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36Contentsii
BackgroundAs the use of e-mail has increased among the internet community, incidents related to the misuse ofe-mail and the abuse of e-mail systems have also risen. Likewise, discussions about how to address andresolve problems associated with such misuse have increased. Some more prominent e-mail abuseproblems include spamming, spoofing, and unwanted mail forwarding. In all these cases, the resources ofyour company or institution may be used by others without your permission. The SMTP exits described inthis document are designed to address some of these problems by allowing you greater control over eachpiece of mail that's processed by the SMTP server.To understand why you might choose to use one or more of these exits, and determine which ones willbest address the particular problems at your installation, explanations for some common e-mail terms areincluded here:SpammingSpoofingMail ForwardingSource RoutingSpamming is the act of sending mail to a large number of e-mail addressees and isoften compared to the term “junk mail” used to describe similar activities performed viapostal services. Spam is a piece of mail that is perceived by its recipient(s) to beunsolicited and unwanted.Spoofing is an act performed by a client sending mail. The client connects to a mailtransfer agent (the SMTP server is one example) and falsifies the information it'srequired to provide. Spoofing is usually done in order to cause mail to appear to havecome from somewhere else.Mail forwarding is the process of receiving and sending on mail that is directed to yourmail server but is ultimately destined to somewhere other than your own site; this is anormal and accepted practice in many cases. Mail forwarding becomes a problem whenthe originating site “bounces” its mail off an intermediate site so that the destination sitedoes not reject that mail, because mail from the originating site is not desired.Source Routing is a particular type of mail forwarding. In this case, the specified mailrecipient path includes a mailbox and a list of hosts. The list of hosts is the route, or theinformation about how to get to the final destination. Mail is passed from one host inthis list to the next, until it is delivered to the intended recipient.For example, suppose a host receives a message with the SMTP command:RCPT TO:where ALPHA and BETA are the list of hosts, and joe@GAMMA is the mailbox. The mail willbe sent to ALPHA, then to BETA, and finally to joe@GAMMA.In the past, this technique was often necessary to accomplish mail delivery, and someinstitutions may still need to use source routing because they have not migrated to usingmore current practices. However, source routing is now strongly discouraged by many“experts” among the internet community, especially as mail processing technologieshave improved over time.The SMTP EnvelopeTo better understand the parameters associated with the SMTP exits and how the exits work, it'snecessary to understand SMTP transactions.Mail is sent by a series of request/response transactions between a client, the “sender-SMTP,” and aserver, the “receiver-SMTP.” These transactions pass (1) the message proper, which is composed of aheader and body (these are separated, by definition, by the first blank line present in the message), andBackground 1
Page 1: IBM®TCP/IP SMTP User Exits Support
Page 5 and 6: ►►──QUIT──────
Page 7 and 8: SMTP Commands ExitIn addition to th
Page 9 and 10: Client Verification ExitIt is somet
Page 11 and 12: When this entry is processed, the f
Page 13 and 14: Because an identical exit parameter
Page 15 and 16: ASSEMBLER Parameter ListNote: Gener
Page 17 and 18: Table 4. Client Verification Exit R
Page 19 and 20: EXITIndicates a mail forwarding exi
Page 21 and 22: Table 5. Mail Forwarding Exit - Sam
Page 23 and 24: ASSEMBLER Parameter ListNote: Gener
Page 25 and 26: User Word 1Provided for use by the
Page 27 and 28: SMTP Commands ExitThe SMTP server c
Page 29 and 30: EXPNIndicates the exit routine is t
Page 31 and 32: VRFYIndicates the exit routine is t
Page 33 and 34: REXX Parameter ListInputsTable 10.
Page 35 and 36: Port number of clientIf the connect
Page 37 and 38: Table 12. SMTP Commands Exit Return
Page 39: ►►──SMSG──server_id─

TCP/IP SMTP User Exits Support APAR PQ14324 VM TCP/IP ... - IBM

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