if your outgoing mail is not going out...try this

t was happening to me. this fixed it.

go to: mail>pref>accounts

then look all the way down at the bottom where
the Outgoing Mail Server menu is. EVEN IF your smtp is showing to be accurate, click on it and then click on edit server list

then remove any server that is not yours. my outgoing mail was a big stall, MAIL was trying to send it out to smtp.mac.atlanticcbb.net

that was not me. as soon as I deleted that false server, which was TRYING to send it via .mac, the accumulated outgoing email shot out like a fleet of jets.