On servers where a catchall has been setup using the qmailadmin web interface, it is possible for postmasters to delete an email account that was setup as a catchall account (in this case; johnsmith@example.com). When this occurs, the .qmail-default file is not updated. Assuming said catchall was already designated prior to removal, mail is accepted for any-random-user@example.com and messages are deferred when delivery to /home/vpopmail/domains/P/earthwire.com/johnsmith is attempted. This can cause the qmail queue to grow over time when you have many users with this scenario.

A problem /home/vpopmail/domains/P/example.com/.qmail-default file:

| /home/vpopmail/bin/vdelivermail '' /home/vpopmail/domains/P/earthwire.com/johnsmith

What a nonexistent qmail user directory deferral looks like;

/var/log/qmail/current:
@400000004b72cd931e35f0ac delivery 5362496: deferral: client_connect:_connect_failed:_2/user_does_not_exist,_but_will_deliver_to_/home/vpopmail/domains/P/example.com/johnsmith//can_not_open_new_email_file_errno=2_file=/home/vpopmail/domains/P/example.com/johnsmith/Maildir/tmp/1265814921.29239.qmailserver.maildomain.com,S=3149/system_error/

A quick solution(s):

OR