Address Book was not designed to be used on a network with multiple users having access to the same list file. Because Address Book keeps its list in memory and periodically saves the list to disk, new records entered, or records edited and then saved by one user, will be overwritten by other users saving their changes.
Many people do, however, use Address Book successfully on a network with multiple users. This is accomplished by allowing only one administrator to have write privileges to the shared Address Book list file. All other users must have read only privileges. This can be accomplished using Address Book's Password Protection feature: there are three levels of passwords. The “Read Only User” password opens and shows hidden lists; the “Full Access User” password opens and shows hidden lists, and allows editing of existing records and creation of new records; the “Administrator’s” password allows setting, changing, and installing lower level passwords. If the Administrator’s password is removed, the other passwords are also removed. Although this is very restrictive, it does guarantee list file integrity.
If you have a situation in which multiple users need to enter new records and edit existing ones, each user should use a copy of the "master" list on his or her own computer. Each user's list can then be updated periodically by using the Merge List File option under the File Menu.
Simultaneous saves to a shared list by more than one user can not occur. A "file open" condition would be detected and an alert displayed.
