What is greylisting

Greylisting is a method for preventing spam sending. This antispam technology used from 2004, initially it was used by some little email services,
but now we know that it's used by some very-popular email services.

We have no special statistics, but about 15% emails (during the last 2 years), and about 25% (during the last 4 month) - that was verified by our
service is secured by greylisting like technology.

There are very lots types of greylisting, but it can be split into four basic parts, email delivery allowed only for:
1) "white-listed IP", white-listed is global for whole email service. 
2) "white-listed domains", white-listed is global for whole email service.
3) "white-listed IP", white-listed is local for each recipient email box. 
4) "white-listed domains", white-listed is local for each recipient email box.

Greylisting and Anti-Greylisting technology

As you can see greylisting 3) and 4) is not trivial and making problems for email verification, up to 50% "unknown" emails. That is why we develop our Anti-Greylisting technology, helping to decrease the amount of "unknown" emails. Our technology is different effective for different email services because greylisting settings are very-very different. Sometimes greylisting can be broken through 15 minutes, sometimes through 1 day...That is why our solution is friendly with the biggest part of email services but is not 100% effective. Our Anti-Greylisting technology implemented in online bulk email validator, we strongly recommend to use it for all verifications.