I found a switch in the settings
The SPF system allows you to specify servers and IP addresses that are authorized to send mail from your domain(s). This feature works to prevent outgoing spam messages.
so we are no longer sending email from emu.arvixe.com
, but from +mx +ip4:188.8.131.52 ~all
I have no idea what all that means, or how it works, but let's see if that makes a difference.