A Global Address List (GAL) is an electronic shared address book which contains usually all people of given organization (company, school etc.). This address book is accessed over the computer network using

LDAP The Lightweight Directory Access Protocol (LDAP ) is an open, vendor-neutral, industry standard application protocol for accessing and maintaining distributed directory information services over an Internet Protocol (IP) network. Directory serv ...

protocol,

CardDAV vCard Extensions to WebDAV (CardDAV) is an address book client/server protocol designed to allow users to access and share contact data on a server. The CardDAV protocol was developed by the IETF and was published as in August 2011. CardDAV is ...

or some other electronic means. The GAL is usually read-only for users. Only administrators add or update the items. Users can search it, look up other people (employees, students, members, etc.) and obtain information such as their email address, phone number, work position and office location. A common usage of a GAL is if the user is writing an email, and knows the recipient's name but doesn't know their email address. The application, such as an email client (e.g. SOGo,

Zimbra Zimbra Collaboration, formerly known as the Zimbra Collaboration Suite (ZCS) before 2019, is a collaborative software suite that includes an email server and a web client. Zimbra was initially developed by LiquidSys, which changed their name ...

or Thunderbird) can look up the email address in the GAL while the user has written only a part of the recipient's name.

Certificates and encryption

LDAP directory can be used also for distribution of user certificates ( X.509,

OpenPGP Pretty Good Privacy (PGP) is an encryption program that provides cryptographic privacy and authentication for data communication. PGP is used for signing, encrypting, and decrypting texts, e-mails, files, directories, and whole disk partiti ...

). So user can query the GAL not only for contact information but also for digital certificate of other users – in order to send them e.g. encrypted e-mails.

References

SOGo DocumentationRFC 4523 LDAP Schema Definitions for X.509 Certificates
– can publish certificates and CRL to LDAP Directory services Groupware Email