The process of migrating eMail from OS X SnowLeopard to Lion has not been quite as simple from some as it might be.
The migration of our Earthlink POP Accounts was straight forward.
The system recognised the configuration properly and the accounts were good to go, so I assumed the other ISP we used would be as well.
Well, we all know that to assume makes an ass out of you and me.
The other ISP uses the same address for both the outbound and inbound mail service... mail.providername.net, and does not use an POP/APOP Authorisation, but instead requires Username & Password authorisation, which means that you have to configure the outgoing mail server manually.
..and TaDa! Success!
All of which we determined by trial and error because, like many ISP's, their on-line support documentation does not match the actual current service configuration.
... and there are several other possible configuration permutations, depending upon which service you're using.
If you're migrating IMAP accounts... that's a-whole-nother-story
But, the moral of the story?
The Bottom Line?
Instead of wasting time swearing at the software or cursing the developers, call your service provider's help-desk and ask for HELP.