rpoyourow said

"An error occurred while sending mail: The mail server sent an incorrect greeting: resomta-po-06v.sys.comcast.net resomta-po-06v.sys.comcast.net Excessive failed authentication, ESMTP server temporarily not available, please contact support." We have no idea what this means. Neither of us have changed anything affecting our log in protocols. What is the matter and what should we do?

"Excessive failed authentication" means that many attempts were made to send e-mail, but the username/password combination were wrong.

The Comcast servers are (correctly), assuming that someone/something is trying repeatedly to send e-mail incorrectly from your Internet connection, and so they temporarily block any attempt to send e-mail through your Internet connection, no matter the computer or device being used.

My guess is that one of the computers, tablets, or phones you are using on your Internet connection is infected by a virus or other malware. The virus is attempting to send e-mail incorrectly (wrong password), causing this.

So you need to check the security on every device. Make sure that your anti-virus and firewalls are working properly and are up-to-date. Then use extra malware scanning programs to find and eliminate malware. I recommend using both Spybot Search & Destroy and Malwarebytes Anti-Malware free versions.

You should also make sure that your WiFi is protected with a password.

Last but not least, know everyone who is using your Internet connection and that they are doing so legitimately.

If you are not sure and need help with security on your devices, then I recommend getting someone else near you to do it.

Thanks for your suggestions.

That didn't work. Just me and my wife, and all devices are protected, checked, mal-wared. Also odd is that it didn't work at all yesterday morning, then worked last night, but wouldn't work again today. Again, receiving is no problem; outbound doesn't work at all.

Comcast is temporarily blocking you from using the outgoing e-mail server, in hopes you will solve the problem on your end. After some time (maybe 24 hours), they re-enable the server for you again.

Then a device using your Internet connection tries a bunch of times to send e-mail with the wrong username/password combination, so Comcast blocks outgoing mail again for another X hours.

If your legitimate e-mail programs are working properly when you are not blocked, then something else (another program, another device, another person), is trying to log in to the outgoing e-mail server improperly, using your Internet connection.

Perhaps someone is hacking into one of your devices. Unfortunately there are lots of ways this could happen. If you have installed remote control/conferencing software like TeamViewer, ShowMyPC, or the like, thet they might be a way in.

I think I'm at an end of how I can help. Maybe someone else here will chime in, but I recommend getting someone to physically check the security of all your devices.