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Some users are trying to send email to certain domains using Exchange Server 2003, but the message is always is rejected and the following message is shown:

5.5.0 smtp;554 Transaction Failed Spam Message not queued

The IP is not in a black list (checked using http://whatismyipaddress.com/blacklist-check and is clean - not listed).

The emails were checked using using smtpdiag ("a troubleshooting tool designed to work directly on a Windows server with IIS/SMTP service enabled or with Exchange Server installed") and the connection using port 25 is ok.

Also, an nslookup with set type=ptr shows (names and IP changed, ">" means I typed something):

C:\Documents and Settings\administrator>nslookup
Default Server: publicdns.isp.net
Address: 10.10.10.10

> server publicdns.isp.net
Default Server: publicdns.isp.net
Address: 10.10.10.10

> set type=ptr

>mydomain.com

Server: publicdns.isp.net
Address: 10.10.10.10

mydomain.com
primary name server = publicdns.isp.net
responsible mail addr = root.isp.net
serial = 2011061301
refresh = 10800 (3 hours)
retry = 3600 (1 hour)
expire = 604800 (7 days)
default TTL = 86400 (1 day)
> 20.21.22.23
Server: publicdns.isp.net
Address: 10.10.10.10

23.22.21.20.in-addr.arpa name = mail.mydomain.com
20.21.in-addr.arpa nameserver = publicdns.isp.net
20.21.in-addr.arpa nameserver = publicdns2.isp.net
publicdns2.isp.net internet address = 10.10.10.11
publicdns.isp.net internet address = 10.10.10.10

Server: publicdns.isp.net
Address: 10.10.10.10

23.22.21.20.in-addr.arpa name = mail.mydomain.com
20.21.in-addr.arpa nameserver = publicdns.isp.net
20.21.in-addr.arpa nameserver = publicdns2.isp.net
publicdns2.isp.net internet address = 10.10.10.11
publicdns.isp.net internet address = 10.10.10.10
> set type=mx
> mydomain.com
Server: publicdns.isp.net
Address: 10.10.10.10

mydomain.com MX preference = 10, mail exchanger = mail.mydomain.com
mydomain.com nameserver = publicdns.isp.net
mydomain.com nameserver = publicdns2.isp.net
mail.mydomain.com internet address = 20.21.22.23
publicdns2.isp.net internet address = 10.10.10.11
publicdns.isp.net internet address = 10.10.10.10
> set type=a
> mydomain.com
Server: publicdns.isp.net
Address: 10.10.10.10

Nombre: mydomain.com
Address: 20.21.22.23

When I test the spf record with http://www.mxtoolbox.com it shows:

TXT mydomain.com 24 hrs v=spf1 a mx ptr ip4:20.21.22.23 mx:mail.mydomain.com -all

Any clues of what's happening here?

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1 Answer

up vote 0 down vote accepted

The unfortunate nature of current anti-spam techniques is that they are imperfect and prone to false positives if the recipient has settings wound too tight. I don't have a specific answer for you but I think there would be value in trying a few troubleshooting steps:

  • Is this happening for all messages to that domain? Or just some?
  • If the sender re-sends the message later, does it go through? (Just trying to determine if block is due to flow-control or is message specific.)
  • Can you send manual tests (for example from the command-line via telnet) and successfully send a message?
  • Did this behavior start recently? Or has this been an on-going issue?
  • Have your users ever been able to successfully send to this domain?

If nothing obvious stands out, I'd suggest collecting a packet capture and examining the SMTP conversation. That might provide clues on when exactly the message got rejected. If not, you'll have some "evidence" you can provide to the recipient mail administrator who can hopefully elaborate on what's going on.

Hope this helps.

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