To remove groups from the Address Book in Outlook you will need to run a PowerShell script to identify all of LawToolBox matters groups and subsequently remove them from the Address Book. This action is persistent on existing groups however any new matters will added to the GAL requiring this script to be run again. 


This script will pull all of the groups that begin with "tb." in the email address of the group and then remove it from the GAL. The second part will again pull the groups and hide them from the Outlook client. Please be aware that while you can remove them from the Address Book and from the Outlook client it will remain in cache for some time until it updates. 


Start PowerShell with Administrator privileges, copy the lines below and paste into the terminal, then Enter.


Set-ExecutionPolicy -ExecutionPolicy RemoteSigned -Scope LocalMachine
#Enter 'Y' when asked
Install-Module ExchangeOnlineManagement
Import-Module ExchangeOnlineManagement
#Use Global Admin account to sign-in (pop-up)
Connect-ExchangeOnline
#Hides Groups that start with tb. from tenant
Get-UnifiedGroup -Filter {Name -like 'tb.*'} | Set-UnifiedGroup -HiddenFromAddressListsEnabled $true
#Hides Groups that start with tb. from Outlook
Get-UnifiedGroup -Filter {Name -like 'tb.*'} | Set-UnifiedGroup -HiddenFromExchangeClientsEnabled $true


You can find the current scripts here