Greylisting to Prevent Spam

All account holders that use email are interested in reducing the incidence of spam. Whether your account is our new Professional Hosting, or VPS Hosting, or a Reseller Hosting account – greylisting may be of use to you. Greylisting is a method of defending email users against spam. A mail transfer agent (MTA) using greylisting will ”temporarily reject” any email from a sender it does not recognize. If the mail is legitimate, the originating server will try again and the email is accepted.

Greylisting is effective because many mass email tools used by spammers will not bother to retry a failed delivery, so the spam is never delivered. If a spammer does retry a delivery after the waiting period has expired, any one of a number of automated honeypots will have had a good chance of identifying the spam source and listing both the source and the particular message in their databases. Thus, these subsequent attempts are more likely to be detected as spam by other mechanisms than they were before the greylisting delay.

The main advantage from users’ points of view is that greylisting requires no additional configuration. You will just be require to go to: You will only notice a delay on the first message from a given sender, so long as the sending email server is identified as belonging to the same whitelisted group as earlier messages. If mail from the same sender is repeatedly greylisted it may be worth contacting us with detailed headers of delayed mail. You can simply email the header details in to our support department for analysis.

When a mail server is greylisted, the duration of time between the initial delay and the re-transmission is variable. Some mail servers use a default of four hours, though most will retry sooner. Most servers have retry rules set to attempt delivery after around fifteen minutes.

To add greylisting to your account please view:


There are 2 comments on “Greylisting to Prevent Spam

  1. Avatar
    John Crumpton April 14, 2009

    When we setup greylisting we thought something was wrong as the number of spam emails dropped to zero! Well worth doing.

  2. Avatar
    Tony Booth May 13, 2009

    Is there prospect of getting user options added to greylisting to allow:
    1 Setting of time to drop greylist entries not used instead of the fixed 36 day limit as at present.
    2 Editing option to flag selected individual greylist entries as permanent whitelist.


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