When I go to https://myaccount.google.com/security there's a section "Apps with access to your account". When I click on it, I see The Bat listed under "Third-party apps with account access" as well as under "Signing in with Google". Do you see that too?
And back in The Bat itself, under Account Properties | Transport | Section:Receive Mail | Button:Authentication, is the authentication method set to OAUTH? (it is for me, and it works).
I volunteer as a moderator to help keep the forum tidy. I do not work for Ritlabs SRL.
The Bat was already listed as a third party app with access, so that didn't need to be changed.
We switched the authentication from "regular" to "OAUTH" and he can now send but still not receive mail.
I really appreciate all of your help. Since I have had multiple Gmail accounts set up in The Bat and not had any problems, and he already had a Gmail account set up, we can't figure out why this one account won't work like the others. We set it up exactly the same. But, I am so thankful that you are giving us some suggestions to try.
Also, the ports on all the Gmail accounts we have are Incoming 995, Outgoing 465. But, the instructions when I checked Gmail as to how to set up your email client says that the Outgoing should be 587. What ports do you have your set at? These are all set up as POP accounts.
Edited: Ann C - 14 December 2020 02:05:23(added more information)
UPDATE: Everything is now working in my husband's new Gmail account. We deleted it and set it up again, exactly the same way. We checked all the settings on Gmail for forwarding POP mail. The only change we made was to have the copies on the Gmail online account be archived after downloading via POP. Other than that, all the other settings were the same. Thank you for all of your help.