What is Greylisting?

Email greylisting is a method of protecting email users from spam. A Mail Transfer Agent (MTA) that uses greylisting blocks a suspicious email with a “temporary rejected” error. In such a situation, a legitimate SMTP server makes multiple attempts to resend a delayed email until it is finally accepted.

Libraesva ESG has adopted greylisting technology. And here it is also important to understand the functions and functionality foreseen by Libraesva ESG.

How does it work?

Typically a server that utilizes greylisting technology generates triple data for each arriving email message:

• host sender IP
• e-mail address of the sender
• e-mail address of destination or receiver

this triple data is then verified with the triplet registered in the database. If this triplet has not yet been registered (registration time is variable), the sender is placed in the greylist for a brief period (10 minutes) and is refused with an SMTP 4xx code. This code corresponds to a temporary error and therefore any legitimate server will retry to send the email.

The Greylisting is efficient because a large part of instruments utilized by spammers does not fall into the resending category, and hence the message will not be sent to the receiver. If the spammer tries to resend the email, Libraesva ESG will accept it and analyze it as usual via the antispam engine.

How Libraesva can help?

Libraesva administration console allows to manually create Whitelist or Greylist, to force the engine to accept or always keep in standby (obligating them to retry) some senders or domains.