Thunderbird with office365: "Request is throttled"

[aragats]

This has been perfectly working for more than 4 years, but starting from yesterday the following message pops up very frequently (mentioning various folders):

The current operation on 'Inbox' did not succeed. The mail server for account 'Work' responded: Request is throttled. Suggested Backoff Time: 182073 milliseconds.

I was doubting this is FreeBSD related, however, a quick Google search with pattern "The current operation" "did not succeed" "Request is throttled" reveals just one result from 2012.
I just rebuilt mail/thunderbird, but didn't get any improvement...

Thanks for ideas!