I have tried below all commands in Exchange power shell, but still users receives the same error message when trying to send on behalf of distribution list. Please help

Get-DistributionGroup "SOperations" | fl name,grant*

Set-DistributionGroup SOperations GrantSendonBehalfTo XXXUser

Set-DistributionGroup SOperations GrantSendonBehalfTo SOperations  (to allow all users in the group)

Error for user:--Delivery has failed to these recipients or groups: You can't send a message on behalf of this user unless you have permission to do so. Please make sure you're sending on behalf of the correct sender, or request the necessary permission. If the problem continues, please contact your helpdesk.

Make sure the user is selecting the Group from the GAL the first time they try and send as another object. 

Keep in mind if you ran both the commands serialially, you would've overwritten the first one with the second one. Did you test sending from the xxxuser or a user in the SOperations group and how long has it been since you granted the permissions then testing the send.

Set-DistributionGroup SOperations GrantSendonBehalfTo XXXUser

Set-DistributionGroup SOperations GrantSendonBehalfTo SOperations  (to allow all users in the group)

Add that particular user under "Managed by" , then user is able to do send on behalf

If you want poweshell, try bellow one

Set-DistributionGroup "SOperations" -ManagedBy "user email address" -BypassSecurityGroupManagerCheck

Regards,

Joby