If a sender sends a message to a valid address and receives a returned message with the error "User unknown," verify the address by using the imta test -rewrite command. Most likely the user entry in the directory is not correct. Retrieve the full directory entry for this user, and verify it. IMTA dirsync can also check directory entry errors. Enter the command:
# imta dirsync -t
If no invalid entries are reported, try running dirsync again with the -v switch, and look at the newest /var/opt/SUNWmail/log/dirsync.trc-* for more information.
Once you've fixed the directory user info, you may run dirsync again, or wait until the periodic incremental dirsync runs. Run the command:
# imta dirsync [ other options ... ]
Finally, check the ownership of all files in /var/opt/SUNWmail/imta/db is set to inetmail:mail. Verify that all the files are writable by the owner.