I’m not an expert on the differences but SSL and TLS are close relatives (for secure transport over the Internet - e.g., HTTPS).  It turns out that Outlook 2003 required a post-SP1 hotfix a while back to support SMTP over TLS.  The 1&1 mail server it seems supports SMTP with SSL on port 25 but only SMTP with TLS on port 587 (the nonstandard port they offer if your ISP blocks port 25).

I just recently did a fresh install of my laptop.  Tonight I installed Outlook 2003 and set up my new 1&1 email account.  Mail wouldn’t send.  Turns out the download from MSDN did not include SP2 (which includes the hotfix).  After installing SP2, Outlook works like a champ sending mail via authenticated SMTP over port 587 using TLS for transport security.

Of course the only thing I’m really protecting is the transport of my credentials between my network and the SMTP server.  The SMTP server will relay my messages in plain text.  That’s one of the fundamental problems with email.  Which brings me back to why the stuff they’re doing at TrustMe is cool (www.keepemailsafe.com), but now I’m just starting to sound like a shill.