Sending emails via Thunderbird doesn't work

I recently had to unsubscribe to Xfinity internet and cable due to unavailability, but kept my email account.  I receive email on my PC just fine over Thunderbird, but cannot send emails via Thunderbird.  This is new, as I've been using Thunderbird for years with no trouble.  When I send, I get a notice right away that Thunderbird has connected to the server--then after a long delay I get another message that the message has been interrupted.  My wife uses an Ipad to email also on xfinity, and messages receive and send with no trouble.  Anyone have any ideas?

PKojola