lmtp usernames with -

Hello

I have a problem with lmtp delivery to usernames with '-' char. Everythong after - is ignored.

when delivering to test-test2 the error message is.

User doesn't exist: test

I suspect this is a sideefect of auth_username_format = %Lu I have tried %Ln without success.

Imap works without problems for those users.

How can I disable this mapping for lmtp and use verbatim username for lookup.

Thanks in advance for any answers.