GAL Segmentation in O365

GAL Segmentation is the process of segregating the Global Address List based on some criteria where in users will see only the information available in their GAL as specified by the Administrator using the Address book policies.

This GAL segmentation is mainly used in Exchange Hosted environments where multiple clients will be hosted inside the same Exchange organization but will have different GALs through Address book policies that eventually makes them to feel like they belong to two different Organizations.

Microsoft added this concept of Address book policy with Exchange 2010 Sp2 and it's also added to Office 365 environment for Exchange Online now,

Review this TechNet article and Exchange Team blog for understanding more on this

http://technet.microsoft.com/en-us/library/hh529948%28v=exchg.150%29.aspx

http://blogs.technet.com/b/exchange/archive/2013/02/14/address-book-policies-jamba-jokes-and-secret-agents.aspx

Finally, Read this below blog post from FLEXECOM which clearly shows you how GAL Segmentation works with Office 365 Environment and step by step procedure on how to create address book polices and assign it to the users and much more in detail.

http://www.flexecom.com/gal-segmentation-in-office-365/