"/did_1+0+0/ " meaning ?

[george]

qmailI don't know understand the message "/did_1+0+0/" in /var/log/syslog file when 
qmail success delivery
Example:
May 30 11:06:38 www2 qmail: 991191998.879928 delivery 9: success: /did_1+0+0/

Anyone can tele me?
Thank you!