What is the appropriate command for maildrop to handle qmail virtual users?

I am trying to use maildrop to handle delivery of mail for the virtual domain domain1.com for qmail. My default (real system) user is user1.
     I am using courier's authuserdb and can successfully login to sqwebmail with virtualuser1. I can see email (delivered with another mail delivery program). The maildir for virtualuser1 is
/home/user1/users/virtualuser1/Maildir
     virtualuser1 has an entry in the file
/etc/courier/userdb/domain1.com
     of a format that begins with
[email protected] ....

    My present attempt to extract the username from qmail's [email protected] is as follows.
|/usr/bin/maildrop -w 90 -d \`echo \"\$DTLINE\" | sed -e \"s/Delivered-To:\ //\" -e \"s/user1-//\"\`
    which does not work.
    I am not sure why I am using the variable $DTLINE as my notes here are old and incomplete.
    Regardless, the above line does not work.

    What is the correct command line that would allow maildrop to extract the proper username for virtualuser1 and deliver mail to the Maildir as set in userdb?