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Outlook receiver profile


Throughout the deliverability landscape, there are Internet Service Providers (ISPs) that are classified as Tier 1 and Tier 2. Tier 2 being smaller cable providers like Comcast, Cox, Charter, etc, and Tier 1 being global providers like Gmail, Verizon Media Group and Apple. One of these Tier 1 providers is Outlook.

Outlook recently went through a merger with Hotmail and now has the Hotmail domains under the Outlook/Microsoft infrastructure. When segmenting for Outlook domains be sure to include,,, and With so many domains, both .com and localized (.ch, .de,, etc) Outlook tends to make up about 10% of a marketer’s email list.

Key characteristics

Spam complaint-driven: deferrals and blocks

Some of the key characteristics for Outlook as a receiver is that they are heavily focused on the number of spam complaints an IP range or domain generates. Typically, when the spam complaints occur in an above-average number, Outlook will begin to defer mail from being accepted. The more often these deferrals happen, the more they tend to result in soft bounce timeouts. Aside from spam complaint-driven deferrals and rate-limits exceeded, Outlook will very rarely bounce mail for other reasons.

Microsoft SRD votes

Something that is unique to Outlook as a receiver is what’s called a “Microsoft SRD Vote”. SRD stands for Sender Reputation Data and these votes are crowd-sourced from actual Outlook participants. Once random participants are placed within the program, they are shown emails from various mailers. They vote on whether the mail should be properly classified as spam or not spam. The feedback then goes to the Outlook’s proprietary SmartScreen filter as it is trained to classify spammy content and mailers. While reports from one user solely cannot create junk status and requires additional feedback from other users in the SRD program, the more of these “junk” votes a mailer’s content receives, the more likely it becomes that their mail will be flagged as spam.


Similar to Google’s Postmaster Tools site, Outlook has created the Smart Network Data Services site (SNDS) for internal monitoring of traffic from sender’s IPs. SNDS reports on any IPs that have an abnormal status such as blocks. It reports on Outlook owned spam trap hits for the 24-hour window, as well as whether the SmartScreen filter is flagging a sender’s mail as spammy or not. The largest ambiguity with SNDS is the legend for reading the SmartScreen filter results. If IPs fall into the “red” at SNDS, that means that greater than 90% of the mail is being flagged as spammy. If the IPs fall into the “green” that means that greater than 90% of the mail is being flagged as “not junk”. If mail falls into the “yellow” the interpretation is that between 11-89% of mail is flagged as being spammy.

One of the frequently asked questions when it comes to SNDS is “if mail is being flagged as spammy, does that mean it is going to the junk folder?” The answer to that is “not always.” Outlook mentions on their website that the outcome of the SNDS filter “doesn't directly represent deliveries to users' inboxes or "Junk e-mail" folders.” Each user has the ability to influence mail flow into the inbox by how they interact with mail on the contact level. For example, the more that a contact moves mail into the junk folder, regardless if the SmartScreen filter says it’s “not junk” the contact’s action overrides the filter.

Best practices for mailing to Outlook

Monitor Outlook recipients and bounce rates

Taking into account the spam complaint-driven deferrals, SRD votes, and filtering solutions in place at Outlook domains, it is imperative that the marketer finds the engagement sweet spot for their mailing audience. More often than not, the unengaged portion of lists spam complain more than the core engaged audience, the marketer should be monitoring the Outlook specific spam complaint rate. The more spam complaints that arise, deferrals and bounces are not far behind. Once those bounces become more regular, the list is opened up too far to unengaged members (openers and clickers). This is also a charge to segment reporting based on the receiving domain so as to get more granular than simply contacts on the message level but rather contacts on the receiving domain level.



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