why am i getting messages on my phone screen from gmail asking for my comcast.net credentials

the message appears on my screen and when i click onto it it sends me to a page asking for user name and password for the comcast email. It has the gmail logo. when i type in the user name and password, it says it can't verify and asks me to change my server settings.
This started happening a few hours ago--no previous problem was noticed by me. I can not get rid of it.

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