I have been getting a lot of account verification errors on Gmail and Yahoo with the newest update, it seems to happen with Gmail more than Yahoo. When the notification pops up and is selected it goes to the account verification screen in k9 and it connects with no problems after tapping next.
Some more details would probably help, like which version? “Latest” would be 6.508.
Also do you use POP3 or IMAP? Which type of authorisation?
I use both Gmail + Yahoo accounts with IMAP + OAuth and haven’t had any issues 
Using IMAP and not sure on OAuth. One last piece of information, It only seems to happen after setting with screen off for a little time and to make it harder to troubleshoot it is intermittent.
A screenshot of the incoming/outgoing server settings would probably help (make sure to obfuscate any private info) and it would also show you if you’re using OAuth or not.
Make sure to exclude K-9 from your device’s battery optimisation and allow “unrestricted background data” as well.
Ok, it is using OAuth. Battery Optimization was on, turned it off. I think that may have been the cause. I will monitor it for a bit and see. If that doesn’t fix the issue I will post a screenshot of the connection details.
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