Exchange Online Mail-Enabled Security Groups

In Microsoft 365, mail-enabled security groups are best created via PowerShell rather than the Microsoft 365 Admin Portal. This is because this type of group tends to not be visible after creation.

Connect-ExchangeOnline
New-DistributionGroup -Name "Group Name" -Type "Security" -Members "[email protected];[email protected];[email protected]" -Alias "Group-Name" -Description "List of users" -MemberJoinRestriction closed

After creation, the group will be visible in the Exchange Admin Centre immediately and will have a default email address of Group-Name@[tenancy].onmicrosoft.com.