SMTP: How Reply Chooses a From Address

The information in this article applies to:

• Microsoft Mail Gateway to SMTP, versions 2.1 and 3.0

SUMMARY

Microsoft Mail Gateway to SMTP saves the From field seen in the envelope part (RFC-821) of an incoming message to use in case the Microsoft Mail recipient wants to reply to the message.

MORE INFORMATION

The Microsoft Mail postoffice database has one From field. This causes the SMTP gateway to choose one of the four possible SMTP From fields to save in the postoffice database. The four possible From fields are explained in the Background section below.

By default, the gateway saves the RFC-821 Mail From information in order to ensure that non-delivery replies will always work properly. In most cases, this information is the same as the RFC-822 From field. All four From fields can be viewed in the SMTP gateway log file, SMTPGATE.LOG. You can see the RFC-821 From field in the beginning of a message transmission, on the line that begins:

   [rx] MAIL From:...

   Header: From:...

Background

SMTP From information is covered by two RFCs: RFC-821 and RFC-822. RFC-821 keeps From information in the Mail From field. This "gives the reverse-path which can be used to report errors." (RFC-821 Section 3.1). RFC-822 has From information in three fields:

• Sender: for "notices of any problems in transport or delivery....NEVER in a reply." (This field is only present if its contents are different from the From field below.)
• Reply-To: for replies.
• From: for replies if no Reply-To field exists. (RFC-822 Section 4.4.4)

For Replies:

• Reply-To
• From

• Sender
• From
• Mail From

RESOLUTION

Version 3.0.9 of SMTPGATE.EXE adds a switch to give an SMTP gateway administrator the choice of which From field to use. If you use the -F switch, the gateway will save the From field in the RFC-822 headers, rather than in the Mail From field. This means replies will always work properly. However, a non-delivery notice might not work if the RFC-821 From field is different from the RFC-822 From field.

The RFC-822 From field was chosen because if the Reply-To field is saved in the From field, the recipient will never know who actually sent the mail. To prevent misleading the recipient, you can use the -F switch to save the From information.

STATUS

Microsoft has confirmed this to be problem in version 3.0 of Microsoft Mail Gateway to SMTP. This problem was corrected in version 3.0.9 of SMTPGATE.EXE. If you do not have version 3.0.9 (or later), you can obtain the latest version from the Microsoft Software Library (MSL). Download SMTPGW.EXE (S14223), a self-extracting file, from any of the following services:

• Microsoft's World Wide Web Site on the Internet

        On the www.microsoft.com home page, click the Support icon.
        Click Knowledge Base, and select the product.
        Enter kbfile SMTPGW.EXE (size: 231849 bytes) 
                               , and click GO!
        Open the article, and click the button to download the file.
  
  

• Internet (anonymous FTP)

        ftp ftp.microsoft.com
        Change to the Softlib/Mslfiles folder.
        Get SMTPGW.EXE (size: 231849 bytes) 
  

• The Microsoft Network

        On the Edit menu, click Go To, and then click Other Location.
        Type "mssupport" (without the quotation marks).
        Double-click the MS Software Library icon.
        Find the appropriate product area.
        Locate and Download SMTPGW.EXE.
  

• Microsoft Download Service (MSDL)

        Dial (206) 936-6735 to connect to MSDL
        Download SMTPGW.EXE (size: 231849 bytes) 
  

   ARTICLE-ID: Q119591
   TITLE     : How to Obtain Microsoft Support Files from Online
               Services

REFERENCES

RFC 821, SIMPLE MAIL TRANSFER PROTOCOL RFC 822, Standard for ARPA Internet Text Messages