Greylist
What is a greylist?
A greylist is a term used in email management, referring to senders that are neither completely blocked (blacklisted) nor completely allowed (whitelisted).
This technique helps combat spam by temporarily delaying emails from unknown senders.
Why is greylisting important in email marketing?
These lists have several practical uses.
For example, spam control and communication quality
In this sense, using greylists in email marketing is essential to maintaining the quality of communication.
Helping to filter unwanted emails, ensuring relevant messages reach their destination.
Relationship with email marketing campaigns
This is the area where you need to be most careful, because although greylists aren’t spam lists, they can also affect your sends.
If emails are not delivered or are delayed, it can negatively impact your campaigns. Especially if the campaign you’re sending needs to be immediate.
How greylisting works
Greylisting is an effective technique used to combat unwanted email (spam) in email systems.
Its operation is based on the principle of temporarily delaying emails from unknown senders.
Let’s see how this works step by step:
First contact from an unknown sender
When an email server receives an email from a sender for the first time (i.e., an unknown combination of sending server IP address, sender address, and recipient address).
In these cases, the email server applying greylisting will temporarily reject this email.
This bounce is not definitive.
It’s more like a “try again later” request.
Response from the sending server
Legitimate email servers, upon receiving this temporary rejection response, will automatically schedule a new attempt to send the email after a short period of time.
This delay period varies, but can generally last from several minutes to an hour.
Second attempt to send
It happens when the sender’s email server tries to send the email again after the delay period and contacts the same email server.
The latter recognizes that the email is probably legitimate and allows it to be delivered to the recipient.
Greylist registration
Once an email from a sender is accepted after delay, future messages sent via that combination of server IP, sender address, and recipient address will no longer be delayed.
This combination is added to a kind of “temporary whitelist” to prevent future delays.
Spam Management:
Many spammers don’t use sophisticated email servers and don’t retry sending emails after a temporary rejection.
Therefore, greylisting can be very effective in reducing spam volume, since many unwanted emails simply aren’t sent again.
Conclusion
Paying attention to what happens with the campaigns we send is essential.
If we notice that the delivery of many messages is delayed, it is possible that a greylist is affecting us.
In these cases, an immediate review is necessary to prevent us from being included on a spam blacklist later.