My suggestion would be to check the spam folders on your email accounts to see if the missing email is being detected as spam by the email server.
I don't know about me.com or gmail.com, but you will have to use the webmail access for your comcast.net email to check that since Comcast does not have imap access for their residential customer email. You should be able to access it from the email icon on the comcast.net portal page once you are logged into that page. If that does not work, try using the url »xfinityconnect.mail.comcast.net/
(I have to use this url, but it only works after you have logged into your account). Once you have access to the webmail page, you can see anything that is in the spam folder. If you find that there is frequently false positive spam for specific email addresses or domains, you can go into the email preferences and setup filters that will force email from specific sources (or with specific content) to always be delivered to your inbox (or you can just turn off spam detection entirely). I have had to do this with Comcast email, AT&T/Yahoo email, and even email delivered to my own domains. It is just the nature of how email and spam detection/prevention works...and fwiw, I have had to put firstname.lastname@example.org into a spam whitelist or filter rule for just about every email server I use.--
We can never have enough of nature.
We need to witness our own limits transgressed, and some life pasturing freely where we never wander.