You have probably heard of blacklisting, where access to a service is denied to a group of entities. And you have heard of whitelisting, where access is exclusively granted to a group of entities, possibly bypassing normal protection measures. So, what would greylisting mean?<\/p>\n
In the context of e-mail, greylisting is a term describing a procedure used to protect your e-mail from unwanted messages.<\/p>\n
Spammers often send messages to generic email addresses. They do not have a database of subscribers, but rather \u2018shoot in the dark\u2019 \u2013 aiming for commonly used names and prefixes such as Anna@… or mail@… created on popular domain names. The majority of the recipients do not even exist. The result is spam senders get a lot of bounce-back messages and non-deliverables. The spamming server will not attempt to send the message again as it does not do any kind of error checking.<\/p>\n
Here lies the difference with a normal outgoing mail server \u2013 unlike a spammer, for a normal server a failure to send a message would be a cause for concern. That normal server will try to resend the message automatically (without necessarily notifying the user) 7 minutes later, then another 7 minutes, then a couple hours later and so on.<\/p>\n
Greylisting recognizes that difference in behavior between different outgoing mail servers and changes the behavior of the incoming server. When someone sends you a message for the first time, the greylisting server will reject it automatically and wait for a retry. If a second such message appears, your server will know it was not sent by a spammer, and will accept the message. Moreover, it will put it on a temporary whitelist. The more messages you successfully receive from that sender, the more trusted they will be from your server.<\/p>\n
Greylisting is a technique, very successful at filtering spam – a rule, integrated at an infrastructural level which cannot be enabled or disabled individually per account. All major providers use greylisting nowadays, including Combell.<\/p>\n","protected":false},"excerpt":{"rendered":"
You have probably heard of blacklisting, where access to a service is denied to a group of entities. And you have heard of whitelisting, where access is exclusively granted to a group of entities, possibly bypassing normal protection measures. So, what would greylisting mean? What is greylisting – generally speaking?…<\/p>\n","protected":false},"author":1,"comment_status":"closed","ping_status":"closed","template":"","format":"standard","meta":{"footnotes":""},"ht-kb-category":[44],"ht-kb-tag":[],"acf":[],"_links":{"self":[{"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/ht-kb\/3515"}],"collection":[{"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/ht-kb"}],"about":[{"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/types\/ht_kb"}],"author":[{"embeddable":true,"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/comments?post=3515"}],"version-history":[{"count":1,"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/ht-kb\/3515\/revisions"}],"predecessor-version":[{"id":3516,"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/ht-kb\/3515\/revisions\/3516"}],"wp:attachment":[{"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/media?parent=3515"}],"wp:term":[{"taxonomy":"ht_kb_category","embeddable":true,"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/ht-kb-category?post=3515"},{"taxonomy":"ht_kb_tag","embeddable":true,"href":"https:\/\/www.combell.com\/en\/help\/wp-json\/wp\/v2\/ht-kb-tag?post=3515"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}