> And that is, this method of dealing with spam, or what?
You are partly right, but it probably refers to the ACL.
A little explanation.
We have a corporate newsletter to the branches, which we want to send only nekotoryh our servers. The rest of the access should not be.
MX record a.ru located on the original domain.
We want to send with the exterior Ah-PI addresses a.b.c.d, c.d.e.f