Normally, mailDBupdate reads the subdirectories of the /aliases and /users directories in the root NetInfo domain. Aliases are written to the aliases file, and login names for user accounts are written to the passwd file. Alternate domains for both aliases and user accounts can be specified with the -a and -u options.
When invoked with the -A option, mailDBupdate appends to its output files. It does not check for duplicate entries that may already exist in the files.
The output files are normally written in /LocalLibrary/Images/People, but an alternate directory may be specified following the -o option. However, note that Mail only searches for aliases and passwd files in /LocalLibaray/Images/People.