This issue is best dealt with in the postfix mailing list; however, there are a few things required to have any hope of understanding what is going on:

0) which version of postfix are you running (you didn't indicate the version of centos) 1) postconf -n 2) are you running any of the daemons in chroot (see master.cf) 3) grep 553E01079AD /var/log/maillog

Finally, I am not exactly sure what problem you are seeing (I didn't send any data, but I appeared to pass the check that you were seeing). So, I don't think that this is a postfix problem, but rather a transient DNS issue (which is why postfix responded with a temporary error (451) which causes a retry). Troubleshoot your DNS plant, and not your SMTP plant.

telnet 200.46.249.100 25

Trying 200.46.249.100... Connected to mail.elpanama.com (200.46.249.100). Escape character is '^]'. 220 *** Bienvenido al Sistema IMSS *** HELO eastern.pmei.com 250 mail.elpanama.com MAIL FROM: steve@pmei.com 250 Ok RCPT TO: email.elpanama@elpanama.com 250 Ok QUIT 221 Bye Connection closed by foreign host.

Steve Friedman

On Mon, 4 Jun 2007, Erick Perez wrote:

Hi, I have been given the task to check on a postfix server that presents the following error: Let's say you use your hotmail account and then send a message to one of my users. The postfix program running on the server responds:

Jun 4 10:21:25 mail postfix/smtp[29744]: 553E01079AD: to=email.elpanama@elpanama.com, relay=localhost[127.0.0.1], delay=54253, status=deferred (host localhost[127.0.0.1] said: 451 Unable to complete command, DNS not available or timed out (in reply to MAIL FROM command))

first, why is giving me a timeout? and second, why in the response the to= field has the domain name?

what things can i see in the main.cf?