> It sounds like you have a human problem on your hands, not a technical one. I would think about how to get an updated SPF into their DNS. If the boss said "just make it work" then to me that means to call the clients and hand hold them through figuring out who hosts their DNS records and how to open a support ticket or reset their self-service web portal login password, or whatever else the client needs to do to get those records in there.

Exactly my point