mail password issues on Lion 10.7.5 Imac
The password-entered properly, many times-is not being accepted on my Imac. Not problems with 3 other Macbook pros
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That's why. You have 2FA. Lion is too old it doesn't understand what 2FA is.
My suggestion is to update to OS X El Capitan, How to get old versions of macOS - Apple Support. It should recognize the 2FA there.
Backup before installing.
Cheers,
Jack