5 minute server response delay when using qmail SMTP, "AUTH LOGIN" on port 25

[petersonj]

I am new to centOS, plesk, and qmail but have been administrating many Ubuntu and Red Hat servers for quite some time. I have never had a problem quite like this. I just started using a new hosting company and everything went well but... When ever I use / enable SMTP authentication in the Plesk panel the server takes around 5 minutes to respond after the "AUTH LOGIN" command is issued from any email client. To verify this I manually started a SMTP session with my server, see below; as can be seen as soon as the "AUTH LOGIN" command is issued the server stops responding and eventually after about 5 minutes the "334 VXNlcm5hbWU6" response finally comes. After that everything is quick. I also tested this procedure locally on the server itself and it works fine there is no delay. This only happen on port 25, if I enable port 587 it also works fine. I am using some older technology that needs SMTP with AUTH on port 25. I am baffled.... Thanks in advance.

Trying 70.32.73.39...
Connected to mail.startechplus.com.
Escape character is '^]'.
220 startechplus.com ESMTP
EHLO
250-startechplus.com
250-AUTH=LOGIN CRAM-MD5 PLAIN
250-AUTH LOGIN CRAM-MD5 PLAIN
250-STARTTLS
250-PIPELINING
250 8BITMIME
AUTH LOGIN

<<-------------------------------- 5 Minute Delay!!! Why???--------------------->>

334 VXNlcm5hbWU6
quit
334 UGFzc3dvcmQ6
quit
535 auth failure
quit
221 startechplus.com
Connection closed by foreign host.

I have search the forums and my config files look correct. I am not having the same problem that others have posted about 30 second delays before the banner is shown and -Rt0 fixes. I have disabled spam filtering.

 

[Josh Elson]

Make sure you have a reverse DNS entry setup for your server IP address