When you use exchange with outlook then the client configuration works almost magically.
This is also possible for non-exchange mail servers.
The simplest solution is the new software called automx
Together with two entries in your dns you get automatic configuration.
The system covers automatic configuration for Outlook and Thunderbird (and all others using the same configuration discovery).
You specify what pop/imap/smtp services should be used and what ports and ssl/tls encryption should be used as default.
We at aarboard have now enabled this autodiscovery service for all our client domains.