554 resomta-h2p-554993.sys.comcast.net resomta-h2p-554993.sys.comcast.net ESMTP server not available

Hello, @user_zwfqki and sorry for the inconvenience. Looks like that error is the result of your outgoing email server having issues establishing a connection. Are you on a VPN or have your firewall settings set high? I would temporarily disable those to see if it fixes the issue. Also, too many errors with username/password verification can cause this issue as well. Ensure your full Comcast email address and password are entered correctly in your email client and saved. Ultimately, I would check your email setup for Outlook.  

To set up third-party email clients for your Xfinity Email, first, allow access to these programs on the Xfinity Email website. Then, use the following settings:

• Incoming Mail Server: imap.comcast.net (Port: 993 with SSL ON or 143 with SSL ON)
• Outgoing Mail Server: smtp.comcast.net (Port: 587 (SMTP) or 465 (SMTPS))
• Encryption: TLS (or SSL if TLS isn't available).

For specific email programs like Outlook or Apple Mail, follow the detailed setup instructions provided by Xfinity.

For more details see: https://www.xfinity.com/support/articles/email-client-programs-with-xfinity-email