HELO RFC 2821: Telnetting to Gmail's SMTP servers

Telnetting to SMTP port of a mail server is a common troubleshooting task to test SMTP connectivity and mail flow that most of us do ever so frequently. After the initial HELO/EHLO command, you issue a MAIL FROM command that provides a return path to the receiving server - generally the SMTP address of the sender e.g. [email protected]

With most servers, MAIL FROM:[email protected] works.

Today I was testing some X-header functionality with Google's Gmail service, after having performed similar tests against Exchange Server 2007 (Beta 2), Exchange 2003, and Hotmail. However, when I issued the MAIL FROM command when testing with Gmail, it threw up a syntax error! I use this almost several times a day, and never have I seen a syntax error being thrown up on MAIL FROM or RCPT TO.

Out of curiosity, I decided to lookup RFC 2821 to figure out if there was something I wasn't doing right or that Gmail was enforcing in its zeal to be strictly RFC-compliant. As it turns out, the RFC does require addresses to be enclosed in "<" and ">" brackets!

Specifically:

The first step in the procedure is the MAIL command.

MAIL FROM:<reverse-path> [SP <mail-parameters> ] <CRLF>

This command tells the SMTP-receiver that a new mail transaction is starting and to reset all its state tables and buffers, including any recipients or mail data. The <reverse-path> portion of the first or only argument contains the source mailbox (between "<" and ">" brackets), which can be used to report errors...

I've never come across this particular issue with almost any MTA that I remember testing against... entering the addresses with those brackets seemed to work.