If you think your email software is having problems connecting to the server, the best way to test this is to use Telnet to manually connect to the server.
This can be done within the Command (CMD) prompt within windows:
> telnet mail.yourdomain <port>
If you see
Connected to mail.ourdomain
Escape character is '^]'server: 220 mail.example.co.uk ESMTP server ready
However, if you just see
Then your IP could be blocked. If this happens, please open a ticket including your IP