Comcast email not receiving MFA messages

Many services now require multi-factor authentication. For some reason emails sent to my Comcast.net address often disappear and never reach my mailbox. In some cases they show up after a long wait (10-15 min.) when the code sent by the service already expired. This has been going for a long time. I use web browser to access my email. I request that the issue be fixed the sooner the better.