Two types of address lists are supported in the Web Client.
Your personal address books, which consists of contacts you maintain. A Contacts and an Emailed Contacts address book are the default address books.
A Global Address List (GAL), some times called Company Contacts, is available to users within your organization. The GAL may contain convenience features such as distribution lists to facilitate communicating with an entire department.
You cannot edit GAL entries. You can, however, import an address once it appears in email you send or received. You can add additional contact information when the name is in a list in your Address Book.