I just started having this problem yesterday, Thursday, September 15, 2022, I’m in eastern USA. I use the Avast anti-virus program. eM Client was failing to sync with Google, and also with two other email accounts I have, all IMAP: freeshell.org and 1-voip.net. I first followed the steps listed here, removing my eM Client account from Google, then restarting eM Client. I got the popup in Firefox from Gmail asking me to authorize eM Client. I did that. Still, syncing not working on all 3 accounts. So, I temporarily stopped all the shields in Avast. Upon restarting eM Client, one outgoing email to my Gmail account got sent, and the freeshell and 1-voip accounts now synced. But still, Gmail will not sync my inbox or other folders that contain incoming mail.
I have the Evolution email client configured in a Linux VM. I just started that, and it is syncing with Gmail without issue. So this is an eM Client problem only.
[EDIT 9/17/22] Today, both my Google and other email accounts were again failing to sync. Knowing that temporarily disabling Avast anti-virus at least allowed the other account to sync, I again disabled Avast and clicked Refresh in eM Client. All my accounts successfully synced, including Google. I opened a ticket with eM Client - I bought a lifetime license. I’ll update that with the observation that for me at least, this appears to be a conflict with Avast. For those using AVG, note that these two merged awhile ago, so they’re basically the same now. Hopefully this will help somebody.
[EDIT 9/19/22] I finally got eM Client working again, with all Avast shields running. I had to change my account settings from:
host: imap.gmail,com
port: 993
security policy: Use SSL/TLS on special port (legacy)host: smtp.gmail,com
port: 587
security policy: Use SSL/TLS on special port (legacy)
Email receipt works fine with these settings, but sending was failing. I changed SMTP to:
host: smtp.gmail,com
port: 587
security policy: Force usage of SSL/TLS
And now I’m able to send and receive again. I opened a ticket with eM Client, after spending the $10 for the privilege, but was essentially told “talk to Avast, this is their problem”. I figured this out myself. I doubt I’ll get my $10 back.