To create a global address book, first create an address global book for one user, populate it with the names you want to be on the global list, then replace the existing global address book with those values. The specific steps would be:
1) Log into Open WebMail as a specific email user.
2) Click on the addressbooks icon.
3) Type in the name of a new address book.
4) Click on the Add button.
5) Click on the name of the new address book.
6) Add the entries to your address book.
7) SSH into your VPS as the root user.
8) If you developed the address book as a Linux user based email, execute the following command in the SSH session:
cp /home/username/.openwebmail/webaddr/addressbookname /var/www/cgi-bin/openwebmail/etc/addressbooks/global
9) If you developed the address book as a virtual user email, execute the following command in the SSH session:
cp /var/spool/vmail/domainname.com/openwebmail/username/.openwebmail/webaddr/addressbookname /var/www/cgi-bin/openwebmail/etc/addressbooks/global
In the above examples, change "username" to the actual user name. Change "addressbookname" to the actual address book name. Change "domainname.com" to the actual domainaname.com.
Whenever you want to add new names to the global address book repeat these steps (skipping steps 3 and 4).
One additional note: It is possible that future updates to Open WebMail may overwrite the global address book. Just repeat these steps (minus steps 3 and 4) if you lose the global address book with an Open WebMail update.