FIXED! MacOS 10.14.4 Update Breaks Gmail in Apple Mail

Like many Mac users, after taking an automatic update to 10.14.4 in early April 2019, my dad found that Apple Mail could no longer send or receive mail on a Google Mail account. 

The messsage "Google requires completing authentication in Safari" kept popping up when Mail was opened.  That took you to a Safari GMail login session - but that failed to work, even with the right password, so it went round and round in an endless loop...

I managed to fix it via the following steps:

1. Quit the Apple Mail program.

2. Turn off content blocking in Safari.  Also delete all cookies and all cache contents.

3. Turn on "less secure access" in Google: https://myaccount.google.com/lesssecureapps .  (It is not less secure!  That seems deliberately misleading to me....)

4. In Apple's System Preferences / Internet Accounts  pane, delete the Google account, then add it back.

That seems to fix it.  Possibly not all of those steps were needed.

All in all, this was not very impressive from Apple. But in the interests of balance, perhaps I should mention that I had similar issues (never resolved) trying to make Microsoft Mail on Windows 10 work with Gmail.  I have to say, the Thunderbird mail client just works - whether it's on Mac, Windows or Linux - despite the Mozilla team's budget being a tiny fraction of that enjoyed by Apple and Microsoft.