SMTP: How SMTPGATE Processes Incoming SMTP Messages (115493)

This article was previously published under Q115493

The following steps outline how SMTPGATE.EXE processes incoming SMTP messages. The files created and used by SMTPGATE.EXE are also described.

1. From the RFC 821 information, we extract MAIL FROM and RCPT TO lines up to the DATA command and put them in the SMTP_IN.ENV file.
2. From the RFC822 information, we append all header lines, the message text, and attachments after the DATA command and put them in the SMTP_IN.822 file.
3. The gateway translates the header part of the SMTP_IN.822 file.
4. At the same time, it copies the header (filtering out the Receive lines if the -T switch is not on) to the API_OUT.TMP temporary file. The gateway closes API_OUT.TMP and records its size.
5. API_OUT.TMP is reopened and appended with the body of SMTP_IN.822.
6. The gateway creates the TO_NC.API file.
7. The API_OUT.TMP file is copied into TO_NC.API.
8. The body of SMTP_IN.822 is appended to the TO_NC.API file and the attached files are UU decoded.
9. SMTP spawns SMTPPUT.EXE, which uses TO_NC.API as its input file for the Microsoft Mail postoffice. For more information on errors, query on ERROR:SMTPPUT here in the Microsoft Knowledge Base.