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Spam Filters

By default, any new mailboxes you create will have Medium spam filtering. You can change this to any setting from None up to Highest on a per mailbox basis. You can also set up a global spam filter from the global section in your panel and this will be applied to all your mailboxes.

When an email is rejected by the spam-filter, our server will refuse to accept it from the sending server. This server should return this to the sender meaning no emails will be lost using the spam filter — they will instead be “bounced” back to the sender.

The default Medium setting should work well for most purposes. If you find that you are receiving a lot of unwanted email at the Medium setting, you may want to consider the High setting instead. Increasing the spam filter setting will reduce the amount of spam that gets through, but will also increase the risk that some legitimate email may be returned to the sender. Using the Highest setting is not recommended as it carries a significant risk that legitimate email may be rejected.

From time to time, we will review and update the filters for each of these settings. At the moment, these settings correspond to the following:

None

No attempt will be made to filter unwanted emails.

Low

• Reject emails from senders which break the SMTP protocol in a specific way in order to send bulk emails faster (unauthorized SMTP command pipelining).
• Reject emails with a badly-formed envelope sender address (e.g. missing a domain).
• Reject emails with an envelope sender address which doesn't exist.

Medium

In addition to the checks from the Low setting, this rejects emails from specific mail servers which are listed on our local blacklist. This list is constantly updated based on our customers' reports of spam.

High

This adds blanket single-stage open relay filtering using the ORDB plus open proxy filtering using the Blitzed Open Proxy Monitor as well as rejection of emails from servers listed as abusable by the Distributed Sender Blackhole List. It also rejects emails from IP addresses listed in the Spamhaus Block List of known spammers and spam-support services.

Highest

This includes all the checks made for the High setting but also adds:

• Rejection of emails from servers with broken DNS (missing or mis-matched reverse DNS record).
• Rejection of emails from servers which announce themselves with an invalid or non-existent name.
• Rejection of emails from exploitable computers listed with the eXploits Block List.
• Rejection of emails sent directly from dynamically allocated IPs listed with the SORBS DUHL.