dovecot lmtp thinks that "disk quota exceeded" is "internal error"

[Arkadiusz Miśkiewicz]

2.2.36 (not migrated to 2.3 yet) reports such problem:

> Nov 13 15:50:58 mbox dovecot: lmtp(xxx): session=<ACYRCtLk6ltiEQAALZVUYQ>, Error: open(/var/mail/xxx/mailboxes.lock1bf6ad16b7b8b703) failed: Disk quota exceeded
> Nov 13 15:50:58 mbox dovecot: lmtp(xxx): session=<ACYRCtLk6ltiEQAALZVUYQ>, Error: Couldn't create mailbox list lock /var/mail/xxx/mailboxes.lock: file_create_locked(/var/mail/xxx/mailboxes.lock) failed: safe_mkstemp(/var
> /mail/xxx/mailboxes.lock) failed: Disk quota exceeded
> Nov 13 15:50:58 mbox dovecot: lmtp(awypior): session=<ACYRCtLk6ltiEQAALZVUYQ>, msgid=<db663455902e1b3faa53f344dc353870 at xxx>: save failed to open mailbox INBOX.Spam: Internal error occurred. Refer to server log for more informat
> ion. [2018-11-13 15:50:58]

Looks a bug to me since disk exceeded is not a internal error. Shouldn't
lmtp return over quota info instead of error?

-- 
Arkadiusz Miśkiewicz, arekm / ( maven.pl | pld-linux.org )