Spam filtering

  • Last updated on: 2018-01-26
  • Authored by: William Loy

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 additional infrastructures. Spam email is also used to phish sensitive and valuable information from companies and to trick people into transferring money. Knowing how to defend against spam and phishing attempts is the first step to keeping 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 several industry best practice techniques to block email spam coming from known disreputable sources. This comprises 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.

The following techniques are some of the methods used by Rackspace Email 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 blacklist senders at both the domain and mailbox level, so that any mail matching the blacklist is blocked.

Filtered Email

If mail passes the blocked email checks, we apply advanced content filtering to verify whether it is considered spam. Content filtering combines many techniques to analyze email structure and content, and creates key indicators that identify patterns in email. These indicators are combined with industry-wide feedback from email providers across the internet about reported spam, phishing, and viruses. The end result is an accurate, adaptive, and evolving content filtering system that is highly effective at removing spam.

The filtering system does not apply only to the sophisticated spammer. This system scans all incoming and outgoing mail traffic regardless of sender or intent. Our filters flag only message content that has been deemed as spam by the whole of the internet community.

Outbound messages

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

Note: Outbound messages are likely scanned by the recipient’s mail provider. Each provider has its own policies for flagging and filtering spam.

Inbound messages

When a legitimate message is flagged as spam, follow these recommendations:

  • Always “unflag” or mark legitimate messages as “Not Spam.” This is the most effective method for improving the reputation of the sender and is a long-term solution.

  • Advise the sender that they are being flagged as spam and provide them with Best practices for sending person to person email.

  • Add the sender to your safelist. For more information, see Manage Safelists at Rackspace Cloud Office.

    Note: Using a safelist ensures that the messages from the sender are delivered to your inbox, but it does not remove a spam flag from a message.

If a message has been delivered to your inbox that you consider to be spam, report it by moving the message to the spam folder.

Warning: Rackspace Cloud Office does not forward any message that is flagged as spam, regardless of whether it is safelisted. If the message is sent to an alias, contact, group list, or distribution list, it is considered to be forwarded and is not delivered if the message is flagged as spam.


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