Mail addresses with quotes + Postfix

[Philipp Berger]

Dear all,

I have a working setup with Postfix + Dovecot, storing users in a MySQL
table.

I ran into problems setting up and using a mail address like
a"@"b at mydomain.tld, which by RFC should be valid, but leads to problems
in Dovecot. From my debugging, I can see that on the lookup, Dovecot
replaces %n with "a" (quotes added by me) and %d with "b at mydomain.tld"
(quotes added by me). So the original quotes are gone, and the
domain/user split is incorrect.

I am not sure of Postfix passes the address without quotes to Dovecot or
whether Dovecot can not handle quotes correctly, but I was hoping that
someone with more insight into Dovecot could help me out here.

System Info: Debian 9, Postifx 3.1.6-0+deb9u1, Dovecot 2.2.27-3+deb9u1
Postfix master.cf for Dovecot:
dovecot unix  -       n       n       -       -       pipe
  flags=DRhu user=virtual:virtual argv=/usr/lib/dovecot/dovecot-lda -f
${sender} -d ${user}@${nexthop}

I am grateful for any hints :)

Thank you in advance, kind regards,

Philipp