Knowledgebase: Email Issues
Greylisting and email delays
Posted by VIRTBIZ Support - Stuart on July 05 2011 05:19 PM
VIRTBIZ customers are protected by a number of spam-fighting techniques; one of those techniques is called Greylisting.

With the VIRTBIZ implementation of Greylisting, any email that is received from a remote IP address is "deferred" - that is, the remote email server is told that their message will not be immediately accepted, but to come back later. A delay of several minutes is then implemented. In most cases, if the sending email server is compliant with RFC standards, the sending server will try again after the delay and at that time the email message will be accepted without further delay. Once that occurs, the IP address of the sending server will be automatically whitelisted for a period of several hours, which means that no further delays will be imposed.

If the sending email server is NOT RFC compliant, which is the case with many senders of spam, then it is likely the sending server will not try back again, since the main goal of a spammer is to send as many messages out as quickly as possible, without high regard for accuracy or standards compliance.

Greylisting should not have a major impact on the reception of legitimate email, and is really only designed to help curb "drive by" spam.

There are a few mail systems that do not properly follow the email protocols as defined by the RFC standards specifications. Due to this failure to follow the standards, bounces may be generated from their sending server when they shouldn't. The most notable one is some older versions of Novell Groupwise. Chances are, the people who are getting back bounces for the mail they send you are using a provider that is running one of these old broken versions of mail server software. The best solution is to have the people getting the bounces get in contact with the system administrators of their email system, and have them upgrade to a version that is standards compliant.

Some broken email servers include:
Novell Groupwise 6.0
ISMail 1.7.1 and prior
InterMail 4.0
Kerio MailServer 5.0.5
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