Same issue with Comcast (Xfinity) and Gmail not accepting PASSWORD

Thank you for your time. It did what I could deleting the related OLD passwords in Keychain, but it still doesn't let my MAC email app use its current password; I have updated the password in my Google account under Gmail settings. I can use Gmail in my browser; yet I prefer my email program for various reasons.

My MAC no longer has Keychain Access Firstaid (I noticed this is another problem discussed on this forum). Is it safe to delete every application password in Keychain that ends with authentication.token?

I cannot reset my ports to your suggestions when I get the password rejection warning. System demands a "Path Prefix" and closes when I do not have that. I have a MAC Air 2011 (macOS High Sierra). When Google suddenly appeared as a server in my email program (after security updates in early 2018), it also made copies of all my folders. Every month, problems worsened, and now I cannot even delete or rename my folders that are under Gmail. Completely do not understand how Google can interfere with its own Gmail!

Well that was interesting - LOL :). To test, I had to use my own email address to test the MAC mail app. Then I sent test messages to myself. 2 tests are in the "new account" mail & 3 tests show up in my usual account mail. And, I now have only Google mail folders with contents on both accounts. My Gmail folders in usual account are empty! I'm done. Have a great weekend!

Reply #2 - So since my Gmail folders were empty, I made that server inactive under Account Preferences. I was afraid to do that before because I thought it would delete all of my files (emails). So I just fixed the original problem. Wish I could remember where I saw others with this issues to ask them about it ... oh well.