Mac Mail won't send messages

I'm using Mac Mail 4.5 on Mac OS X 10.6.7. Every 3 or 4th email I send gets hung up. The send icon just keeps cycling. Eventually, sometimes, an hour later, a message pops up to say my outgoing server SMPT timed out. it doesn't make sense: these messages can be as short as two words with no attachments, and yet they don't work. Then the next one works, no problem. I've never had email do this: it's very frustrating. I can send the same message on my web mail and it goes out immediately. Any help to resolve this would be appreciated.

I'm having the same problem and I'd sure like to know how to fix it.
My Mac Book Pro is only about 3 mos. old and has had all of the OS updates.
Russ