Issue: You need to allow mail from outside senders to all or a large set of Distribution Groups using the Exchange Management Shell rather than modifying each group one by one using the GUI Exchange Admin Center or Management Console.
Use Management Shell commands to search for any distribution groups or dynamic distribution groups that match a phrase and modify the Outside Senders setting.
Note: you will need to specify your group name you want to search for followed by a “*” wildcard in all of the example commands.
Commands to create and test a search query before modifying any settings:
Get-DistributionGroup -identity GROUPNAME*
Get-DynamicDistributionGroup -identity GROUPNAME*
Command to enable outside senders on a set of Distribution Groups:
Get-DistributionGroup -identity GROUPNAME* | Set-DistributionGroup -RequireSenderAuthenticationEnabled $False
Command to enable outside senders on a set of Dynamic Distribution Groups:
Get-DynamicDistributionGroup -identity GROUPNAME* | Set-DynamicDistributionGroup -RequireSenderAuthenticationEnabled $False