Apple Mail not sending messages

Hi all, since last night, my Mail does not want to send any messages, it can however receive messages! Just to be clear, I've googled the problem and I've tried everything that they suggested me, including:

1. making sure that the outgoing mail server are using default ports(25,465,587)
2. clicking mailbox -> synchronize all accounts
3. clicking mailbox -> take all accounts offline, then mailbox -> take all accounts online

I have got into this situation before and it was fixed by doing number 3... but now it doesn't want to do this anymore =(

btw I have three accounts in my mail, two of them are gmail accounts (another one is my work email). Any idea how to fix this? I am on snow leopard 10.6.2!

 

ok, apparently i tried one more thing and it worked. It was clicking window -> connection doctor and click network diagnosis... strange.