comcast.net emails won't send

my mac mail will no longer send email from my @comcast.net emails. I either get "Connections to the server “imap.comcast.net” on the default ports timed out.

Select a different outgoing mail server from the list below or click Try Later to leave the message in your Outbox until it can be sent.

Then it shows my 2 different emails which both say offline (but I am receiving mail)...then it says to fix my server settings, which I try to do but they are exactly as comcast says they are supposed to be.