As I mentioned in my previous post, I recently had to define certain Exchange mailbox properties in order to cleanup the Global Address List for our users, specifically the Company value in each user's Exchange properties. To do this, connect to Office365 using the Azure Active Directory Module and run:
Set-User UserPrincipalName -Company "Microsoft"
Of course, utilizing PS doesn't save as much time if you have to bash out each user individually, so export your user mailbox names to .csv from O365, groom the list (if needed) and input the following:
Get-Content -Path c:\LocationOf.CSV | Set-User -Company "Microsoft"
Though I only needed to define the Company for each mailbox, I've already utilized the Set-User cmdlet to define other properties. Explore the other parameters available by running Get-Help Set-User, while connected to O365. Also note that you must be assigned the appropriate permissions from within the EAC.