On 9 Sep 2019, at 16.17, Philipp Faeustlin via dovecot <dovecot@dovecot.org> wrote:
It is not recommended to rely on local-part case, but it is indeed case-sensitive. And this is to avoid such issues that postfix supports address cleanup/canonicalisation before forwarding mails to dovecot.
RFC 5321: "Local-part = Dot-string / Quoted-string ; MAY be case-sensitive […] While the above definition for Local-part is relatively permissive, for maximum interoperability, a host that expects to receive mail SHOULD avoid defining mailboxes where the Local-part requires (or uses) the Quoted-string form or where the Local-part is case-sensitive." And therefore “receive liberally” policy that wants to assume case-insensitivity should single-case the address IN THE COMPARISON. The local-part MAY be case-sensitive, but in general I don't know any mail addresses where the case matters. Thus it is hard for me to understand, why this comparison of the vacation address is case-sensitive. Whether the final recipients address is also treated case-insensitive.
If this has to be case-sensitive to be RFC compliant, then please create an option for admins or users to change the behavior to an case-insensitive comparison.
Just change auth_username_format = %Lu to make all addresses lowercase. That should solve your problem. Or if you REALLY REALLY want to have case-sensitive userpart, then use auth_username_format = %n@%Ld
Sami