Having mentioned GREYLIST, we need to describe and explain this word. “Greylist” is just as the same function as whitelist and blacklist. Generally speaking, it is a way to categorize email addresses that are suspicious and unfamiliar. If we make a definition technically, we can say:
Greylist 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. Servers for mass email spam, on the contrary, usually do not have such sophisticated features.
How Does Greylist work?
SMTP rules state that the graylist server filters unknown email servers and gives the sending server “temporarily rejected” feedback. Legitimate SMTP servers retry sending after a 15-minute delay by default, with constant retries.
If a graylist filter considers an email suspicious but lets it through after a retry delivery, the next emails will go through without delay. This is because the graylist server remembers the sender’s name and other caches. Thus, it whitelists them without any additional settings from the user.
Another positive aspect of the graylist is that sending temporary errors is a cost-effective measure for MTAs. Because its performance does not require much CPU (central processing unit) power and memory, unlike most other spam filtering programs.
But there are two drawbacks to graylisting. One is that the default delay can be well over 15 minutes in the case of a poorly set up sending server. This can irritate recipients if they are used to the instant nature of email. Another disadvantage is that junk mailers adjust to greylisting and queue spam emails for redelivery, which weakens the anti-spam approach. In any case, it increases the mail delivery rate to some extent and also prevents the mail from going to spam.
How to Prevent Email Greylisting
1. Keep healthy domain reputation
Maintain a healthy sender can reduce your bounce rate and keep you away from greylist and even blacklist to some extent.
2. Don’t abuse your IP-Address
A good IP reputation will minimize your chance of getting greylist.
3. Allow unsubscription
Many reasons may cause users to intend to unsubscribe. But without allowing them to do so, there is no other option but to mark the email as spam. (This is true. When I want to unsubscribe a newsletter, but it does not have an unsub option. I will mark it as a spam or totally trash.) If a sufficient number of users mark your emails as spam, then your IP address reputation will suffer and the blacklist filter will consider your emails as suspicious.
4. Use a real sender’s name while signing up your email
A real existed name, such as [email protected], can help you to build a trustful relationship with your audience and also improve your open rate.
5. Avoid using stop-words
You may confuse about what is so-called “stop-words”. “Stop-Words” is just like “Buy”, “Free”, “Cheap”, “Hurry”… These words may alarm greylisting filters that an email is not trustworthy. Be extremely careful with emails that are expected to be instantly delivered like welcome, transactional, confirmation, etc.
6. Format the headings and the message correctly.
Format the heading and content of the message according to the HTML standards and RFC 5322.
To know about what is greylist is the best way to avoid being graylisted. But, the key to keeping a “good” list is to send quality content to your audience. If you want to trick or fool your users, the result is that you won’t get anything back from them. Even worse, “throwing good money after bad”. So, when you treat your audience as a REAL people and they will regard you as a friend.
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