Apple Maill won't send

I am using Apple Mail  3.2 and OS 10.5.2.  Mail worked like a charm at
the beginning but I suddenly can't send.  All the settings are by the
book. However, the SMTP setting indicates "off line" but I am on a DSL
connection. I have clicked "Take All Accounts On Line" and Take All
Accounts Off Line" but nothing works. Where do I look?

I am sending this with Eudora.