Re: So...
So your UK based business is so tight that it relies on free mail services from a US based business. Recommend that as a business you use business grade services rather than cheap residential grade services. And while you're at it I also recommend you put a little effort into finding out what services you're getting. Reading your contract would be a start.
I work for an ISP and I'm constantly annoyed by business customers who pay for residential services and then moan that they're not getting business services.