No SMTP greeting from remote mailer

[stwman11]

Software version: WHM 10.1.0 cPanel 10.2.0-C88

When connecting to one site, I am not able to receive an SMTP greeting. I test it by:

telnet mail.siteiwanttosendmailto.com 25
Trying xxx.xxx.xxx....
Connected to wsip-xxx-xxx-xxx-xxx.ok.ok.cox.net (xxx.xxx.xxx.xxx).
Escape character is '^]'.

The IP address of the site is returned, but no 220 code is returned. Telnet then times out. The maintainer of the site reports no problems from anyone else, but he might not know. We've traced the packets and it looks as though I'm sending acks after the initial handshake, but they're not being received. His system is NAT'd, but from a different server running Postfix at the same colo, I have no problems.

Please let me know what other information I can provide to help resolve my issue.

Thanks,

Steve

[chirpy]

I'm a little conused Is the server you are telneting on port 25 to your cPanel server? If not, then the problem is at the other servers end and there's nothing you can do about it unless you have access to that server. If you do have access, is it running exim on cPanel?

[stwman11]

The server I am telnetting to is a Postfix box.

I am testing from a Postfix box to the friend's Postfix box from my Postfix box and my cPanel box. It works when going from my Postfix to his Postfix, but not from my cPanel to his Postfix.

So, it works from Postfix to Postfix, but not from cPanel to Postfix.