Windows 7: Outlook 2010 Won't Send

Since upgrading, I can't send from my Work account. It just times out. The account is IMAP connected by SSL. No problems when I used 2007 and I just sent from my phone so I know the account is working. Settings haven't changed and are correct. I've tried disabling all add ins.
Any ideas?

Check if antivirus is interfering. Disable antivirus check of outgoing mail.

It's definitely not my AV. It just won't connect to to port 443 (SSL). 2007 worked no problem. Problem only happened since upgrading today.

Try sending with SSL off.

Won't work. It will only connect to the server using SSL.

Can you test connectivity to port 443? It may be blocked by a firewall or some network settings.

It's not. Like I said, all was fine under 2007 and nothing has changed except I now use 2010. The firewall's not blocking anything, the account's working because I can send on my phone. The only change is 2010. I even deleted the account and started again. Same problem. Can receive but not send. It only happens on this account. Gmail and Hotmail accounts work.

Yes, but gmail and hotmail would be using different outgoing ports.

Do you have an active VPN connection? This will interfere with your outgoing mail.
It would help if you post the full error you receive.

I have similar problem. I can recieve email, but not send. I get "421 Cannot Connect to SMT".
Everything was working perfectly until I upgraded to Office 2010 and outlook 2010 from outlook 2003. I was on the phone with my Verizon DSL ISP tech support for an hour attempting to fix it, verifying all settings were correct and trying different port numbers. I reloaded Office and Outlook 2010, moved some mail to a new .PST file, nothing works.