Strange delay sending email via SMTP on Exchange 2003

emailexchangeexchange-2003smtp

When I try to send email through Exchange 2003 via an SMTP connection, I get a strange delay after specifying the recipient. Here is a telnet log, with a redacted domain name: (telnet mail.xxx.com 25)

220 mail.xxx.com Microsoft ESMTP MAIL Service, Version: 5.0.2195.6713 ready at  Fri, 16 Oct 2009 09:42:20 -0500
HELO
250 mail.xxx.com Hello [172.16.128.42]
MAIL FROM: dms@xxx.com
250 2.1.0 dms@xxx.com....Sender OK
RCPT TO: ttheisen@xxx.com

After a delay of a minute or so, (it seems to vary) I get this:

250 2.1.5 ttheisen@xxx.com

Although the exact delay varies, it's always a significant delay.

However, when I repeat this exact same transaction from our intranet server, there is zero noticeable delay. I'm really more of a software developer than an admin, and I just can not figure this out.

Anyone have any idea what could cause this?

Best Answer

Are you an admin of this Exchange 2003 server, do you have access to the configuration? It could be a few things:

  • Antispam mitigation, some servers add a delay onto the transaction to slow down spammers. AKA Tarpitting.
  • If domain resolution is being done during this process, it is possible there is a problem with resolving xxx.com.
  • Some other custom program or processing done on the recipient email address.
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