I haven't been able to send e-mails when connected to T-Mobile for, oh, a year at least? My e-mail provider (Rackspace) only supports STARTTLS and SSL/TLS, and T-Mobile appears to break the authentication no matter which I choose. I can receive e-mail, but not send it on 465 or 993. As soon as I get home and switch to wifi, everything in my outbox gets sent. It's mighty annoying.
I wasted a bit of time yesterday trying to get a .NET application to send email using SSL/TLS via Rackspace.
It turns out that .NET System.Net.Mail doesn't support implicit SSL, only explicit SSL.
You'd think that Microsoft would have solved that by now. The reasoning:
This is not considered a bug, it’s a
feature request. There are two types of
SSL authentication for SMTP, and we only
support one (by design) – Explicit SSL