Thanks. I no longer get the message about the user not being in the virtual alias table. But there still seems to be a problem.
When I try sending mail thru "telnet localhost 25" etc., everything seems to go ok but the mail doesn't show up when I type "mail" for the user. It is showing up at /root/Maildir/new.
Also, there is no /Maildir directory for some users and no /home/user directory for others.
Update: the mail.log gives this error message: "warning: maildir access problem for UID/GID=1002/100: create maildir file home/sysuser/Maildir/tmp/122401558"