Test Message Works, Real Ones Don't

[Dave]

One of my POP accounts won't send mail. The Outlook 2002
XP error message says the connection to the server was
interrupted, or the connection timed out waiting for the
smtp server.

However, when I go into E-mail Accounts, open the
malfunctioning account and click Send Test Message, the
message sends out, and is received. When I compose a real
message and send it, it does not go out.

I have tried deleting the account and re-creating it, and
have also run Office XP repair installation.

Any ideas?

Background: Yesterday I changed my SBCglobal.net DSL
account and now connect using PPPOE for the first time
with a dynamic IP address instead of a static IP address.
Everything else works fine, including sending mail with
all other of my 5 POP accounts (each using a different
ISP's mail servers).

Thanks,

Dave