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Greylisting – Yet Another Reason Why Emails To Your Customers Are Not Getting Through

What about retention-based emails such as newsletters to your customers or customer service emails?

If you’re sending any mass emails to your customers/leads, then you should know about Greylisting.

Greylisting (sometimes spelled graylisting) is a relatively new yet widely used anti-spam method, implemented by your customers, that automatically “drops” all incoming messages coming from your email-address.

It’s based on the principle that mass email engines don’t behave like a normal mail server. Normal mail servers will, if a temporary error occurs at the receiving end, buffer the email and try again later.

Mass email engines, such as the ones powering common  10 minute mail  affiliate-systems (sending a newsletter from CommissionJunction, ShareASale etc.) or help-desk systems, normally don’t have this functionality built in.

Greylisting generates a temporary error on purpose and waits for the sending server to come back later and try to deliver the mail again. A normal server, waits a while, tries again and then succeeds in delivering the mail. A mass email engine tries one time and then the email is lost forever.

The greylisting mechanism keeps a database of approved senders, each consisting of sender address, recipient address and the IP-address of the sending email server. When a new combination is found for the first time, a message looking something like this is sent back to the sending email server:

451 4.7.1 Greylisting in action, please come back in 00:30:00

Here we can se the appropriate SMTP codes for a temporary error and a descriptive text of what has happened. If the sending email server tries again before the 30 minutes has passed, it will receive a temporary error again:

451 4.7.1 Greylisting in action, please come back in 00:15:00

After the 30 minutes has passed and the sending server tries again, the email will pass and the sender triplet will be registered as “whitelisted” for a configurable duration (30 days or something like that). That means that subsequent emails from the same sender to the same recipient will be delivered without delay.

Greylisting is mostly transparent to your customers, besides for a small delay the first time.

Greylisting is very effective because many mass e-mail tools will not bother to retry a failed delivery, so the email message is never delivered.

If you’re using any third party tools to deliver messages to your customers/leads, make sure these tools are greylisting compatible. Our experience working with clients revealed greylisting as the #1 reason for low open rates.

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