Spam Filtering

Over 90% of all email traffic is spam, although most of it never makes it to your inbox. Spam can cost millions of dollars in business productivity and infrastructure. Spammers also use spam to phish sensitive and valuable information from companies and trick people into transferring money. Knowing how to defend against spam and phishing attempts is the first step to keep your information safe.

This article describes the spam filtering system used in Rackspace Cloud Office.


Applies to: Administrators

For more information about prerequisite terminology, see Cloud Office support terminology.

Blocked email

Rackspace Email uses industry best practice techniques to block email spam coming from known disreputable sources. We stop email we know with a high degree of certainty is not from a legitimate service, including everything from compromised servers to spam cannon services that send unsolicited spam across the Internet.

Rackspace Email uses the following techniques to protect you from spam email:

  • IP block lists provided by reputable services
  • Blocking emails with attachment types known to exploit end-user computers
  • Account admins can add senders to a Blocklist at both the domain and mailbox level to prevent them from reaching your inbox.

Filtered email

If mail passes the Blocklist checks, we apply advanced content filtering to verify spam indicators. Content filtering combines techniques to analyze email structure and content and creates key indicators that identify patterns in email. We combine these indicators with industry-wide feedback from email providers across the Internet about reported spam, phishing, and viruses. The result is an accurate, adaptive, and evolving content filtering system that is highly effective at removing spam.

The filtering system does not apply to the sophisticated spammer. Instead, it scans all incoming and outgoing mail traffic regardless of sender or intent, and our filters flag message content after confirmation by the whole internet community.

Outbound messages

Filtering outbound email protects deliverability for all users on the Rackspace Cloud Office environment. Spam definitions change at a rapid pace, but you can follow certain practices to prevent your message from becoming spam:


The recipient's mail provider likely scans outbound messages. Each provider has its own policies for flagging and filtering spam.

Inbound messages

When a legitimate message flags as spam, follow these recommendations:


Using a safelist ensures that you receive messages from the sender, but it does not remove a spam flag from a message.

If a message arrives in your inbox that you consider spam, report it by moving the message to the spam folder.


Rackspace Cloud Office does not forward any message flagged as spam, regardless of whether it is safe listed. The system considers any message sent to an alias, contact, group list, or distribution list to be forwarded and does not deliver the message if it flagged the message as spam.