As opposed to a blacklist, a greylist is typically considered a “cautionary” list. It marks IPs, URLs, and/or sender information the recipient may want to watch or track. If a sender is on a greylist, they shouldn’t see much (if any) impact on overall deliverability. Another usage of the word “greylisting” is when the receiver returns a transient/temporary delivery error for a message. If the sender attempts to reconnect and send the same message again, the receiver then accepts it. GetResponse is configured to automatically retry transient errors for you for optimal deliverability.