How does the Microsoft Sender Reputation Data (SRD) voting system work?

The Microsoft Sender Reputation Data (SRD) voting system works like this:

  • Microsoft invites email users to be part of a program in which they can vote on randomly selected messages.
  • Users at domains such as and can accept or decline the invitation to be part of this program.
  • If they accept the invitation to be part of the program, they become SRD panelists and periodically receive an email that has a subject line of [Microsoft Spam Fighters] Junk or not?
  • These messages include an original message that was delivered to them as a subscriber.
  • Panelists are then asked to classify the message as Not junk email (an email they want) or Junk email (an unwanted email that should not be delivered to their inbox). They are then prompted to confirm their selection.
  • Email is presented for classification within 12 to 24 hours after the message was originally delivered to them.
  • Microsoft aggregates the votes and transmits the counts each day to Return Path for Certified senders.

Note: Random samplings of email are extracted and selected to present to panelists prior to having any anti-spam technology applied during the delivery process. This allows for responses to be obtained for email regardless of whether it was delivered or where it was placed, such as in the inbox or in a junk folder.

Microsoft uses a sophisticated sampling algorithm to cast and count votes from SRD panelists.  The more volume sent to Microsoft domains, the greater chance the message will be voted on by the SRD panelists. This doesn't mean a sender will receive more negative SRD votes, it just means there is more opportunity for panelists to vote if the message is  junk email or not junk email.  After a certain number of SRD responses, Microsoft decreases the need for further votes (i.e. they have a big enough sample).  Microsoft indicates that each SRD vote is typically representative of 50-100k Microsoft users. This means 5 negative votes represents at least 250k recipients.
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