Email Send from Apple Mail Not working

Email Send/Receive works fine from the Xfinity website.

Using Apple Mail, send mail is broken.  Everything was working fine several days ago.  

Send appears successful but never gets to recipient.  No error messages.

Receive mail on Apple Mail works fine

Connection to SMTP/IMAP is fine.  ID/Passwords are good.

Internet works fine

What is wrong with smtp.comcast.net that it will not complete the send?