Blocking sender
 

In Comcast e-mail, how do you go about blocking a sender?

Don't know if this is the best answer, but you could mark it as spam, or just delete it before opening. If it is from a sales company, you can unsubscribe from receiving their email.
Does that help you?

If you are using MS Outlook, you right click on the email in your In Box. Then select Junk Email, then Add Sender to Blocked Senders List.