smtpmail and name resolution

[dvd]

I can't figure this out; can someone help shed some light for me?

I have no problem sending mail using Gnus from home. However, at
school, when I try to send, I get a "Temporary failure in name
resolution" error. I can send from Thunderbird using the same
configuration (same port, TLS, etc.), and I can connect and send mail
using gnutls-cli. With (smtpmail-debug-info t) the trace shows nothing.
I'm not sure what else I can do to solve or just diagnose the problem.

Thanks for you help,

-David