I've got this error message today even after registering the SPF record in my public DNS succesfully:
Remote Server returned '<mail.mycompany #5.7.1 smtp; 554 5.7.1 Error: need authentication from mail.client.com>'
What I'm trying to do is that I wanted to allow Client.com
who is our outsourced marketing partner to send out promotion email on behalf of my users mailbox in mycompany.com
, I'm using Exchange Server 2013 while the marketing company is on AWS all in cloud.
How to allow this to work ?