This problem also starts to happen with me a few days ago.
Using Avast 2015.10.2.2214 OUTLOOK 2013
All my emails from a given account are blocked. Can't send ou receive.
1. If I disable avast, it immediately starts working fine
2. I read the solution posted by LEO40, but in my Settings there's no such list of accounts and there's no "SSL Settings", but "SSL Scanning" and only a "Scan SSL Connections" check box and a export certificate button.
3. On Mail Settings, there are "Scan inbound", "Scan outbound" and "Scan Newsgroups". If I uncked ALL of them, it also works fine. (if any of three are checked, it doesn't work)
4. If I clean ALL Mail ports on Troubleshooting window, it also works fine. If any of the ports are left, it doesn't work.
It looks like a virus or malware WANTS me to disable mail scanning/shield. So weird !
Please, help me urgent.
Regards,
Carlos