Mailshell Anti Spam Engine - SIEVE Threshold Recommendations

This document details some suggested changes customers should make to the Sieve Filter rules for use with the new Mailshell Anti Spam engine incorporated in MailSite 6.1.22 and above, compared to the Sophos engine in previous versions. This document applies only to customers who have a valid Rockliffe Anti Spam subscription.

Rockliffe customers familiar with the Sophos Anti Spam engine will have become familiar with the scoring of messages between 0 and 10. Our previous threshold recommendations with the Sophos engine were to reject messages scoring 9 and 10 as definitely spam and deliver messages scoring 5, 6, 7, and 8 into the Junk Mail folder as probably spam.

With the new Mailshell Anti Spam engine (shipped with MailSite 6.1.22 and above), the scale changes slightly. Messages are still scored between 0 and 10 and we recommend you set your Sieve Filter thresholds as follows:

• Reject messages with a score of 10 as definitely spam
• Deliver messages with a score of 8 and 9 to the Junk Mail folder as probably spam
• Deliver messages with a spam score of 0 through 7 normally to the Inbox as probably not spam

Typically the Sieve rule to reject messages would be found in the "Server Receive Script" under the server level Sieve Filter.

The Sieve rule to deliver probable spam messages to the Junk Mail folder would typically be found in the "Mailbox Delivery Script" under the server level Sieve Filter.

The above thresholds are intended as a basic guideline. The spam threshold will vary amongst customers. We encourage administrators to take time to become familiar with the spam scoring engine and adjust the Sieve Filters accordingly. There are Sieve Filters you can enable which will append the Spam Score to either the subject or the header of a message. This will allow you to analyze the spam scoring and change thresholds where necessary, allowing you to optimize the Anti Spam engine for your specific message content profile.