What is Greylisting?
Greylisting is an anti-spam technology deployed by mail servers to prevent spam. The receiving mail server tells the sender to please retry to send the email again in X minutes.
A well-configured mail server will attempt to resend an email on different intervals, until it's accepted or rejected by the receiving mail server.
There are many types of greylisting, but the most common one is time-based greylisting, as mentioned above. Each mail server has a different time they greylist the sender for, per email, normally between 1 and 20 minutes.
ZeroBounce deploys break-through anti greylisting technology.
When we encounter any greylisting, we will wait 20 minutes and retry to validate those specific emails. This reduces the number of "Unknowns" you will receive back from us. So, you wait a little longer for your results, but your results will be a lot better. It’s worth noting that ZeroBounce will not charge you for the “Unknown” results.
It doesn't matter how many greylisted email addresses you upload to be validated. Whether it's 1 or 100,000, the processing is only delayed by 15 minutes in total.