When I sended message to some e-mail on server (postfix clients in mysql) I saw that in maillog:
postfix/pipe[5895]: 6201FE37CE7: to=<anton@howtobsd.com>, relay=maildrop, delay=0.04, delays=0/0/0/0.03, dsn=5.1.1, status=bounced (user unknown. Command output: Invalid user specified. )
To senter returned answer from my server:

“This is the mail system at host mail.howtobsd.com.

I’m sorry to have to inform you that your message could not
be delivered to one or more recipients. It’s attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

: user unknown. Command output: Invalid userspecified.

Reporting-MTA: dns; mail.howtobsd.com
X-Postfix-Queue-ID: 8B7C5E37C5A
X-Postfix-Sender: rfc822; anton_paluhin@gmail.com
Arrival-Date: Wed, 28 Apr 2010 15:45:24 +0300 (EEST)

Final-Recipient: rfc822; anton@howtobsd.com
Original-Recipient: rfc822;anton@howtobsd.com
Action: failed
Status: 5.1.1
Diagnostic-Code: x-unix; Invalid user specified.”

I checked maildrop…

#maildrop -v
Copyright 1998-2005 Double Precision, Inc.
GDBM/DB extensions enabled.
Maildir quota extension are now always enabled.
This program is distributed under the terms of the GNU General Public
License. See COPYING for additional information.

I have thought it have to be buit with courier-authlib:

#cd /usr/ports/mail/maildrop && make deinstall
#vim /usr/ports/mail/maildrop/Makefile

uncomment line: WITH_AUTHLIB=yes
…

#maildrop -v
Copyright 1998-2005 Double Precision, Inc.
GDBM/DB extensions enabled.
Courier Authentication Library extension enabled.
Maildir quota extension are now always enabled.
This program is distributed under the terms of the GNU General Public
License. See COPYING for additional information.

It’s Ok!Trying send message and check (in log new problem):

postfix/pipe[59663]: 23414E37EC3: to=, relay=maildrop, delay=24, delays=24/0/0/0.07, dsn=4.3.0, status=deferred (temporary failure. command output: ERR: authdaemon: s_connect() failed: Permission denied /usr/local/bin/maildrop: Temporary authentication failure.)

check rights:
# cd /usr/local/bin/ && la -la | grep maildrop
-rwxr-xr-x 1 root mail 1239752 Apr 29 10:12 maildrop


it is need +s (edit rights) :

# ls -la /usr/local/bin/ | grep maildrop
-rwsr-xr-x 1 root mail 1239752 Apr 29 11:53 maildrop

And after that manipulation maildrop can transport mail in boxes…