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Email Spam

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Port forwarding and MX records

Reputation filters

Encrypted attachments

Grey Listing

Email Monitoring

Internal Email Security

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Per user quarantine area

Reverse DNS lookup & SPF

RFC Compliant emails


Email Throttling

What is Spam

Whitelists and Blacklists



What is Email Grey Listing


Grey Listing is a very effective anti-spam filtering technique that temporarily rejects an e-mail from an unknown sender. The sender is held within a grey list record, typically for a time limit of around 24 hours. Legitimate e-mails will automatically retry sending the message, and the anti-spam filter which grey listed the email will now accept the email as legitimate.

Grey listing has been incorporated into anti-spam filtering software as with many spammers, they use spambots which attempt to send spam to many recipients, but if the spam email is not accepted, spam sources do not retry sending the same message again. Spammers continue to send bulks of spam to other sources. It is too time consuming to wait around and try resending a spam message.

Further Reading

Wikipedia's guide to Grey Listing