@user_555232 - You have reached the right place for help to troubleshoot the sent emails from your Comcast.net email address. We'll get to the bottom of this! A few reasons can prevent your recipients from getting your incoming emails. They could be marked as spam and land in a spam folder. This is due to filtering rules, which we'd want to double check and review to continue receiving incoming messages.

Another thing that comes to mind is to Update your Xfinity Email Port Settings, if you had not already. If you use a third-party email application, you’ll need to configure your outgoing mail server port to 465 or 587, and update the encryption settings of your outgoing mail server from non-encrypted to encrypted settings. If you don't adjust your email settings, you'll still receive emails, but not be able to send emails after the non-encrypted email settings are blocked. Did you notice any error codes or messages when sending email? 

Note: To learn more about using third-party email clients (e.g., Outlook, Apple Mail, Thunderbird, etc.) to access your Comcast.net email address, please see Enable/Disable Third-Party Client Access to Comcast.net Email - FAQs.