Just noticed that for almost two weeks all my outgoing mail using the
OAuth2 account mentioned on my previous mail silently failed to deliver.
While retrieving mail showed an error so it was obvious that something
wasn't right, the fact that outgoing mail is not being actually sent
*without* any kind of warning is quite annoying. Adding to the fact that
the OAuth2 account is what I use for work, this resulted in quite angry
customers complaining about my lack of response.
The same workaround for retireving mail lets outgoing mail to deliver at
last: configuring GMail to accept unsecure passwords and changing
authentication from OAuth2 to plain passwords.
Due to the silent nature of this issue and its implications, IMHO the
severity of this bug should be raised.