I just tested my access to comcast.net email, and I was able to send a message from a bellsouth.net account to a comcast.net account, and then reply to that message with no problems (the messages went through in both directions within a second of clicking the send button).
Unless it was just a temporary glitch that you encountered (or it was spam detection related), you may have a problem with your account, but Comcast residential email in general is not down.
FWIW, the above test was done using web mail, but SMTP and POP3 also seem to be working:
If you are still experiencing problems, post again and provide some more details on what you mean by "comcast email is down", and perhaps you can get some troubleshooting advice.--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.