Some emails take 12 hours to receive or are not received at all in Comcast email inbox

An email was sent to me at 4:21 pm Yesterday.  I just recieved it at 5:27 am (With the 4:21pm time stamp Of the previous day).   More than 12 hours later!  This has been going on for a long time.  When will Comcast fix this?   Comcast email is unusable since it is SO UNRELIABLE.  The email was sent to me from a non-Comcast email server.

Fix it Comcast or discontinue your email service because it does not function!  I was wondering all night why this person did not respond to me.  Turns out they did but their sent email took 13 hours to arrive in my Comcast inbox.