smtp problems

My outgoing email stopped working today on all 3 devices that I use for my comcast email.   Incoming mail is working fine, but outgoing mail is saying that my user name or password is incorrect.   I have not changed any of my settings, and double checked that they were all correct.   Restarting does not help.  I changed my password incase maybe my account was frozen due to a security breach or something.  That did not help.  I believe something is wrong on comcasts end, or with my account.