First, a definition of the term “International Email Delivery” for all non-US residents: International email delivery is about getting an email delivered to an US email address, while being located outside of the US (within the US=national, outside of the US=international, get it?).
Now that you know what I am talking about, you have probably already guessed what the problem is: international email delivery is shaky. Lots of US-based people and businesses implement some kind of IP-geolocation based mail filtering. If some IP database says your IP address is somewhere outside of the US, your mail is not delivered.
Many US residents are often unaware of this, as this policy is implemented by their Email service providers without their knowledge. While it makes sense to assume that a plumber based in Rolling Meadows, IL, is unlikely to receive Email messages from Poland, others might be using an Internet service hosted in Poland, and this filtering policy renders their email address useless for this service.
Some mail servers are straight-forward about location-based filtering, and state the reason for non-delivery openly:
550 country IP access denied
Other servers are more enigmatic, leaving room for interpretation:
How to interpret this answer? Maybe the server does not like the country of origin, or maybe the requested email address simpy does not exist? At least, it is an answer, other servers might not even bother to accept a connection if they do not like the originating IP address.
In all these cases, the email address might actually work, if the right conditions are met, but because our Email validation service is intended for customers worldwide, we try to be on the safe side and flag addresses with potential international delivery problems with the “317 Server Reject” reply.
In the past weeks we have spent a lot of effort in refining our detection algorithms and databases, so we can now detect mail servers with international delivery problems more safely and faster than before.