{"id":77139,"date":"2023-12-26T20:53:53","date_gmt":"2023-12-26T20:53:53","guid":{"rendered":"https:\/\/mailrelay.com\/glossary\/greylist\/"},"modified":"2026-10-15T12:57:54","modified_gmt":"2026-10-15T12:57:54","slug":"greylist","status":"publish","type":"glossary","link":"https:\/\/mailrelay.com\/en\/glossary\/greylist\/","title":{"rendered":"Greylist"},"content":{"rendered":"\n

A greylist is a term used in email management<\/strong>, referring to senders that are neither completely blocked (blacklisted)<\/strong> nor completely allowed (whitelisted)<\/a>. <\/p>\n\n

This technique helps combat spam<\/a> by temporarily delaying<\/strong> emails from unknown senders.<\/p>\n\n

Why is greylisting important in email marketing?<\/h2>\n\n

These lists have several practical uses. <\/p>\n\n

For example, spam control and communication quality<\/h3>\n\n

In this sense, using greylists in email marketing<\/a> is essential to maintaining the quality of communication. <\/p>\n\n

Helping to filter unwanted emails<\/strong>, ensuring relevant messages reach their destination.<\/p>\n\n

Relationship with email marketing campaigns<\/h3>\n\n

This is the area where you need to be most careful, because although greylists aren’t spam lists, they can also affect your sends.<\/p>\n\n

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.<\/p>\n\n

\"Greylisting:<\/figure>\n\n
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How greylisting works<\/h2>\n\n

Greylisting is an effective technique used to combat unwanted email (spam) in email systems. <\/p>\n\n

It works on the principle of temporarily delaying emails from unknown senders<\/strong>. <\/p>\n\n

Let’s see how this works step by step:<\/p>\n\n

First contact from an unknown sender<\/h3>\n\n

When an email server receives an email from a sender for the first time<\/strong> (i.e., an unknown combination of sending server IP address, sender address, and recipient<\/a> address). <\/p>\n\n

In these cases, the email server applying greylisting will temporarily reject<\/strong> this email. <\/p>\n\n

This rejection is not permanent. <\/strong><\/p>\n\n

It’s more like a “try again later” request.<\/p>\n\n

Response from the sending server<\/h3>\n\n

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<\/strong>. <\/p>\n\n

This delay period varies, but can generally last from several minutes to an hour.<\/p>\n\n

Second delivery attempt<\/h3>\n\n

It happens when the sender’s email server tries to send the email again after the delay period and contacts the same email server. <\/p>\n\n

The latter recognizes that the email is probably legitimate and allows it to be delivered to the recipient.<\/p>\n\n

Greylist registration<\/h3>\n\n

Once an email from a sender has been accepted after the delay, future messages from that combination of server IP, sender address and recipient address will no longer be delayed. <\/p>\n\n

This combination is added to a kind of “temporary whitelist”<\/strong> to prevent future delays.<\/p>\n\n

Handling spam<\/h3>\n\n

Many spammers don’t use sophisticated email servers and don’t retry sending emails after a temporary rejection. <\/p>\n\n

Therefore, greylisting can be very effective in reducing spam volume, since many unwanted emails simply aren’t sent again.<\/p>\n\n

Conclusion<\/h2>\n\n

Paying attention to what happens with the campaigns we send is essential.<\/p>\n\n

If we notice that the delivery of many messages is delayed, it is possible that a greylist is affecting us. <\/p>\n\n

In these cases, an immediate review is needed to avoid later ending up on a blacklist for sending spam.<\/p>\n\n

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Reach the inbox, not the greylist<\/strong><\/p>\n\n\n\n

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Related entries<\/h2>\n\n