I have an idea as to your problem.
Either you have some scripts that have the hardcoded username to mail its output to or your sendmail "aliases" file has that user in it.
For the latter, you need to look for a file called "aliases". It is usually in /etc/mail/aliases. Do a "find / -name aliases -print" to find it.
This is the configuration file for how sendmail handles mailing lists based on mail aliases. You may have an entry in there for this user1.
Go ahead and search for an aliases file on your system. On HPUX it is in /etc/mail/aliases.
Once you remove this line from the aliases file, you will need to execute the "newaliases" or sendmail -bi command to update your sendmail configuration.
What may be happening is sendmail still thinks that the user exists because it is in this file even though you deleted them from the system.
