I had the same problem. I fixed it by allowing this on the exchange server, cuz this is the effect i wanted.
This happens you’ve probably set a diffrent email address and senders-name in the general settings of thenewsletterplugin, then it is in the smtp and the exchange server.
You can either set everything the same address and name, or enable this on the exchange via powershell with this command: (without the quotationmarks)
‘Set-OrganizationConfig -SendFromAliasEnabled $true’