This section explains how to allow users to send email on behalf of a group in the Exchange admin center (EAC) in Exchange Online.
Step 1: In the Exchange admin center, go to Recipients > Groups.
Step 2: Select Edit Edit group icon on the Group that you want to allow users to send as.
Step 3: Select group delegation.
Step 4: In the Send on Behalf section, select the + sign to add the users that you want to send as the Group.
Step 5: Type to search or pick a user from the list. Select OK and Save.