[Dovecot] user unknown with deliver

I'm getting user unknown when trying to deliver to Sent folder messages. My master.cf part is: copy2sent unix - n n - - pipe flags=DRhu user=vmail:vmail argv=/usr/lib/dovecot/deliver -d ${sasl_username} -m Sent

But it still won't work. I'm running 1.0.15

pluto postfix/pipe[30934]: 7470890C4DA: to=bcc@bcc.example.com, relay=copy2sent, delay=0.03, delays=0.02/0/0/0.01, dsn=5.1.1, status=bounced (user unknown)