mx1 postfix/lmtp[31831]: A624A43408: to=<aaa@domain.com>,
relay=mx1.domain.com[private/dovecot-lmtp], delay=0.01, delays=0/0/0/0,
dsn=5.1.1, status=bounced (host mx1.domain.com[private/dovecot-lmtp]
said: 550 5.1.1 <aaa@domain.com> User doesn't exist:
aaa@domain.com (in reply to RCPT TO command))

Debug: client passdb out: OK#0111#011user=aaa#011host=192.168.2.10#011destuser=aaa@domain.com#011proxy#011pass=<hidden>
 mx1 dovecot: imap-login: proxy(aaa): started proxying to 192.168.2.10:143/aaa@domain.com: user=<aaa>, method=PLAIN, rip=10.10.10.1, lip=192.168.2.5, TLS, session=<g0fHjx52sucKDAGp>

auth_mechanisms = plain login
passdb {
  driver = sql
  args = /etc/dovecot/dovecot-sql.conf.ext
}

userdb {
  driver = prefetch
}
# The userdb below is used only by lda.
userdb {
  driver = sql
  args = /etc/dovecot/dovecot_user-sql.conf.ext
}

crud_db=# select * from proxy;
   user_    |     host     |          destuser
------------+--------------+-----------------------------
 aaa | 192.168.2.10 | aaa@domain.com