• Synopsis
    This guide explains what greylisting is and how it is set at SyncMyOffice.
  • Applicable to
    All SyncMyOffice 2013 Hosted Exchange accounts.
  • Prerequisite
    You must have an Exchange 2013 account with SyncMyOffice.
  • How to
    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) 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.