Cannot send out mail! Help!

from what I've read here your settings should be:

POP = pop.att.yahoo.com
SMTP = smtp.att.yahoo.com

I don't know about this exact service, but that error means your SMTP outgoing server details are incorrect. Check the ports, address and other settings to make sure they are all right.

I'm having the same problem! I receive e-mail just fine, but I can't ever send e-mail. Except I use Optimum Online as my Internet service. So:

POP = mail.optonline.net
SMTP = mail.optonline.net

I try going into Mail, Preferences, Account Information. On the drop-down menu next to "Outgoing Mail Server," I got to "Edit Server List," and then Advanced. I've looked it up, and I don't think the port is wrong. I don't know what "Use Secure Sockets Layer" is though. I have that checked, so maybe that's doing it? I'm not sure. But I hope we find out!

OK!!

It turns out that the "Use Secure Sockets Layer" option was the problem!! I unchecked it and now I'm able to send e-mail! Try it and this should solve your problem!

i have the same problem except with cox.net

incoming pop.west.cox.net

outgoing smtp.west.cox.net

can receive but send

I have had the same problem with all my non Mobile Me accounts.

I tried everything and nothing worked.

Finally I deleted both accounts having the problem and then started from scratch.

Now they work.

I was very frustrated!!!

This was my only hitch with snow leopard.