'doveadm expunge' with -A and userdb { driver = passwd }

[Grant]

>> doveadm search -A mailbox INBOX.Trash savedbefore 30d
>>
>> but I'm told not to:
>>
>> "If the -A option is present, the command will be performed for all
>> users. Using this option in combination with system users from userdb
>> { driver = passwd } is not recommended, because it contains also users
>> with a lower UID than the one configured with the first_valid_uid
>> setting."
>>
>> I'm using userdb { driver = passwd-file } but I'm guessing that's the
>> same thing.  Am I understanding this correctly?
>
>
> Which passwd-file do you use? Does this file contains any users, which uid
> is lower than first_valid_uid?


Here's what my Gentoo-default auth-passwdfile.conf.ext says:

passdb {
  driver = passwd-file
  args = scheme=CRYPT username_format=%u /etc/dovecot/users
}
userdb {
  driver = passwd-file
  args = username_format=%u /etc/dovecot/users
}

But I don't have an /etc/dovecot/users file.  I also don't seem to
have any mail user uid lower than 1000, but I do have some users above
1000 which aren't mail users (nobody, etc).

- Grant