When i send a mail to the user of messaging server, it returns saying unknown user.

I am trying to add a mail user to iplanet messaging server 5.1, I am able to configure that user from my mail client (outlook) but when i send mail to that user, it returns saying unknown user. I can see that user in LDAP data base/
[246 byte] By [708728] at [2007-11-25 7:09:01]
# 1
This could be symptomatic of the iMS 5.1 server not yet having done a full synch to its alias database of the LDAP server. This is done every 24 hours (default) at 2 or 3 am. You can synch manually by running the "imsimta dirsync -F" command.
708729 at 2007-6-29 17:40:18 > top of Java-index,E-Mail, Calendar, & Collaboration,Sun Java System Messaging Server...