This is really odd.

Some of my clients set up outlook with the correct cpanel settings (IE: mail.theirdomain.com) and when they test the mail settings they can connect to both the incoming and outgoing servers but then the sending of the test email fails.

They cannot send a message... just recieve them.

I am not sure.

1) Check to see if they are authenticating against the server before trying to send.

2) Try sending on an alternate port. Some ISPs block 25 for SMTP

their isp may not allow relay - advise them to try changing smtp to the isp's

I agree with okanagantech...have them change their outgoing smtp server to the one provided by their ISP. Many ISP's are doing this now, and yes, it is a pain in the butt.

Ask them if they have SBC: SBC blocking port 25? (http://www.webhostingtalk.com/showthread.php?s=&threadid=379389) - happened to a number of my customers

Aha! It turned out to be the ISP like you all have been saying.

Thanks Fixed the problem.

:) :)

Well don't you just love it when the problem was not really yours to begin with :)

Yea hahaha... good thing the clients that had the problem were very nice about it. Always makes doing the job easier ;).

bind SMTP to listen on two ports and advise customers which isps block port 25 to connect to an alternatative port?