Comcast no longer supports the SMTP port 25 so if you are using older email client then you must reconfigure the account settings of Comcast. To get rid of the trouble you must use the settings as follows. Incoming Mail Server should be configured as imap.comscast.net, Port 993, SSL must be ON. Outgoing Mail Server should be smto.comcast.net, Port 587. Don’t forget to check the SSL encryption. For authentication Xfinity/Comcast username & password is required. If you setting up a POP3 account, then Incoming Mail Server shall be updated as mail.comcast.net, Incoming Mail Server Port shall be 993 with SSL or 110 without SSL. If the problem persists, it would be better to get in touch with our certified technicians on our toll-free number provided for the instant Comcast email customer support and lighting fast resolutions.