If an Office 365 group has the wrong SMTP address it's not something you can change from the WebUI but it can be done through powershell.



Make sure you have the latest Exchange module installed:

Install-Module ExchangeOnlineManagement

Then use

Connect-ExchangeOnline

complete the login as usual (logging in to the 365 tenant admin documented in 1 pass.



Add the new SMTP address:

Set-UnifiedGroup -Identity "Group Name" -EmailAddresses: @{Add ="GroupName@domain.com"}

Set the new SMTP address as the primary

Set-UnifiedGroup -Identity "Group Name" -PrimarySmtpAddress "GroupName@domain.com"

Remove the old (incorrect) SMTP address

Set-UnifiedGroup -Identity "Group Name" -EmailAddresses: @{Remove="OldGroupName@domain.onmicrosoft.com"}