Some users get permission errors when creating tickets via email after migration to a new host

I had some failing hardware on a machine and had to migrate RT
quickly. I did a mysql dump and upgraded from 3.6 to 3.8 at the same
time.

Everything seemed well, but now some users send emails to the queue
and then no auto-reply, OR they get something like this:

No permission to create tickets in the queue ‘QueueName’

I’ve checked permissions, all seem fine – privileged, unprivileged,
and everyone have been granted CommentOnTicket, CreateTicket, and
ReplyToTicket.

Where should I look first?