Microsoft KB Archive/99713

= SMTP: How Reply Chooses a From Address =

Article ID: 99713

Article Last Modified on 10/30/2006

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APPLIES TO


 * Microsoft Mail Gateway to SMTP 2.1
 * Microsoft Mail Gateway to SMTP 3.0

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This article was previously published under Q99713



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:...

The RFC-822 From field is recorded later in the Header lines, and looks like this:

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 &quot;gives the reverse-path which can be used to report errors.&quot; (RFC-821 Section 3.1). RFC-822 has From information in three fields:


 * Sender: for &quot;notices of any problems in transport or delivery....NEVER in a reply.&quot; (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)

The four From fields can be organized into two categories: those for replies, and those for non-delivery notices, arranged in the order they should be used.

For Replies:


 * Reply-To
 * From

For Non-Delivery Notices:


 * 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, 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
 * The Microsoft Network

On the Edit menu, click Go To, and then click Other Location.

Type mssupport.

Double-click the MS Software Library icon.

Find the appropriate product area.

Locate and Download SMTPGW.EXE.

For additional information about downloading, please see the following article in the Microsoft Knowledge Base:

119591 How to Obtain Microsoft Support Files from Online Services

