Peter,

Our software performs an IP-to-Country lookup using a locally stored database on the company's mail server. I verified that your IP does resolve to a US IP. We released an update to the coutry database in June of this year, and it has the correct information. The previous update, on April 2006, however did not contain any country information about the IPs. Did you just receive the addresses a few months ago?

It is possible that some users do not have the updated geographical database. In that case, the IP would not resolve to a country. Administrators can configure our software to reject emails originating from any country. Unfortunately, against our advice, some admins do also chose to reject IPs that have no country associated with them. We have no control over that, I'm sorry.

I'd recommend you contact the sender's ISP to inform them of the problem.

As a side-note, it is entirely possible that a non-US ISP/company choses to block all emails from the US, if they only perform business withini individuals within their own country. We of course think it's a bas idea (we ourselves would not be able to send them emails...), but there are some strange requirements in some countries...