What is greylisting
This guide explains what greylisting is and how it is set at Sherweb.
You must have an Exchange account with Sherweb
What it is
Greylisting is a recognized and effective tool used to fight spam. It critically limits the amount of emails our servers accept from IPs that have not sent a consistent amount of legitimate mail to our users over a long period of time. Why? Because snowshoe spammers (a new spamming method) are vulnerable in one significant way: the IP addresses they send from only deliver very small volumes of email and never have a long history of sending legitimate email.
How it works
When an email is received from a server that has not contacted our servers in over a week, our anti-spam engine returns a temporary error (SMTP 4XX) asking the sending server to retry in 5 minutes. A properly configured server (following current RFC standards specifically sections 4.2.5 and 188.8.131.52) will respect this request and retry at least 5 minutes later, at which point our server will let the message through. If the server retries before the allowed time, it is blocked for another 5 minutes.
Note: The retry delay is configured on the sending server. This means if it is set to retry in 2hrs, the email will only be resent 2 hours later. Our own servers have no control over the sending server’s delay. Our servers only request to “retry in at least 5 minutes”.
Can I turn it off?
Yes. Please contact our support department to turn off greylisting for your account. Expect to receive more spam messages however.
All Sherweb Hosted Exchange accounts.