While troubleshooting similar connectivity issues, I have found it helpful to use some PHP scripts to perform the basics of verifying that the server is actually capable of connecting to the mail server.
Assuming we cannot connect through the scripts, it would make sense that we would also not be able to connect via SugarCRM.
Some of the common reasons for not being able to connect include:
- Firewall restrictions
- Missing PHP extensions (e.g. IMAP)
- Incorrect account information
Should any of those (or other) conditions exist, the scripts will fail and you know you need to look elsewhere for your solution, instead of within SugarCRM.