Mail not sending

[brianfisher]

OK, I'm using 10.5.7.
Since I upgraded, Mail has been unreliable in sending emails, often not sending them at all.
All my settings seem to be correct, outgoing server and so on. Just get a spinning wheel when I click "send", but the emails never get sent.
Any ideas?

 

[jonesy16]

Have you tried running Disk Utility? (verify disk permissions, then repair disk permissions)