Fighting Spam

Every email marketer would love to know the special sauce that gets their messages directly into the intended recipient’s inbox. However, most marketers, especially those who’ve been doing it for a while, know just how complicated and tricky that task can be.

ISPs give us a few of their secret ingredients here and there, but most scanning and filtering tools that ISPs use are not shared publicly — and for good reason! No one wants spam in their inbox! And if spammers knew all the secrets, they could circumvent them. But for legitimate senders who need to get an email to people who have asked for their messages, sometimes it can be frustrating.

One of the clues Microsoft gives us into how they measure the legitimacy of your email message lies in the headers. In the last few years, they’ve introduced a rating system that determines how spammy or phishy they believe a message to be as well as how likely the sender is to generate spam complaints.

Microsoft’s Anti-Spam Message Headers: SCL, PCL & BCL

As soon as an email message hits Microsoft’s servers, their proprietary Exchange Online Protection (EOP) filtering service scans the message and then inserts an anti-spam report into the message headers. You can read more about all of the different fields and filters they use here, but the three fields that I’m going to focus on today that have helped us understand how messages are being processed are:

SCL = The Spam Confidence Level
PCL = The Phishing Confidence Level
BCL = The Bulk Complaint Level

When opening the message headers you can do a search for X-Forefront-Antispam-Report and find the SCL ratings underneath. BCL and PCL ratings can be found under the X-Microsoft-Antispam section. Here’s a screenshot of the message headers from a message I received in my Outlook account where I’ve highlighted these ratings.


SCL — Spam Confidence Level

After the email is received and goes through the EOP spam filtering it’s given an SCL score. Here’s a breakdown of what each means:

-1 = A special value that means the message is a safe sender and is not spam. This score tells Microsoft to put the message in the inbox.
0-1 = The content of the message was scanned and determined to not be spam. These two scores also tell Microsoft to deliver the message to the inbox.
5-9 = Starting with a score of 5 the message is suspected to be spam and is increasingly suspect to the highest score of 9 which indicates there’s a high confidence it’s spam. Any rating between 5 and 9 means the message should be sent to the Junk folder.

*Note: 2, 3, 4, 7, and 8 are ratings that are not assigned by Microsoft.

For more information, refer to Microsoft’s official documentation on SCL.

BCL — Bulk Complaint Level

BCL ratings range from 0-9 depending on how likely the message is to generate complaints based on historical data. Microsoft says they use both an internal and third-party tool to assign messages a rating — a message that receives a 2 is unlikely to generate many complaints versus a message that receives a score of 8, which is likely to generate a high number of complaints. Here’s the breakdown of BCL ratings:

0 = Indicates the message is not from a bulk sender.
1-3 = This bulk sender generates few complaints.
4-7 = This bulk sender generates a mixed number of complaints.
8-9 = This bulk sender generates a high number of complaints.

For more information, refer to Microsoft’s official documentation on BCL

PCL — Phishing Confidence Level

This rating simply determines how likely the message is a phishing message based on the content. These range from:

0-3 = Not likely to be phishing.
4-8 = Likely to be phishing and marked as suspicious content.

For more information, refer to Microsoft’s official documentation on PCL.

What Do These Ratings Mean?

So what can we take away from these ratings? If you’re having junk foldering issues at any of the Microsoft domains check your SCL, BCL, or PCL ratings. If any of these are high, it could be the cause of the junk foldering. Microsoft doesn’t disclose the specific criteria for how they assign these ratings, but looking at the ratings will let you know what aspect of your email sending you may need to improve to get better inbox placement, be it the message content or your sending practices.

Got questions or comments? Feel free to tweet us or send us a note in our community slack channel. We would love to hear from you!


Microsoft Hotmail Outlook Deliverability Inbox


The Microsoft Outlook inbox is one of the major destinations for most email senders, especially those with large numbers of consumer subscribers. It also has a reputation for being somewhat tricky to get into. Here’s what senders need to know to get the best Hotmail/Outlook deliverability and ensure their messages reach the inbox.

Microsoft’s Outlook service—whether known by the brands Hotmail, Windows Live, MSN, or—uses a combination of factors to determine whether to treat a message as credible or as spam. Like all ISPs, Microsoft’s methods are proprietary. But we know that it analyzes signals that include content, authentication, and domain and IP reputation to create a “trustworthiness” score. Less-than-optimum scores can cause your messages to be “delayed” and/or “spam filtered.”

Best Practices for Hotmail/Outlook Deliverability

Here are six best practices to help maximize Microsoft Outlook deliverability:

1. Warm Up New IPs – Microsoft will only allow 10,000 messages per day for new IP addresses. It will delay the remainder of messages sent from new IPs. Delays are normal when developing an IP reputation.  As your reputation develops over a 2–4 week probationary period, the delays will lessen and eventually discontinue.  The volume of messages that are delivered successfully on the first attempt will rise as Microsoft moves you to a higher reputation level.

Best Practices: to avoid delays, start with 2,000 traffic to Outlook/Hotmail, double every day until you see “RP-001 (DYNAMIC CODE) Unfortunately, some messages from a.b.c.d weren’t sent. Please try again. We have limits for how many messages can be sent per hour and per day. You can also refer to” then slow down the traffic until these delays discontinue.” Note: We highly encourage senders to use their own “custom bounce domain”, “tracking domain” and “dkim sign” with their own domain.

2. Listen and Respond to FBL Complaints – It is important to honor any unsubscribe requests whether a subscriber hits the spam button or the unsubscribe link.  Continuing to send to subscribers that have unsubscribed will harm your reputation with Microsoft. SparkPost applies for and processes Feedback Loop (FBL) complaint feedback for you to minimize this risk.

Best Practices: Add text reminding subscribers where they opted-in to receive your message.  Ensure your messages are relevant and sending at a frequency that the subscriber is expecting.  Remove subscribers that do not engage with your messages.  If as little as 0.5% of your subscribers complain, it will affect your ability to send to your entire subscriber base.

3. Minimize “Unknown User” Hard Bounces – Do you practice positive list hygiene?  Are you sending to an old list that includes a large number of inactive or dead addresses?  Microsoft sees this as a sign of email harvesting or spamming.

Best Practices: Practice list hygiene by maintaining your list.  Purge addresses that have been inactive for 12 months, change the frequency to addresses 3 to 6 months old.  Consistently attempt to re-engage subscribers using different tactics.  Normal unknown user rates average less than 2 to 3 percent.

4. Avoid Spam Trap Addresses – Addresses used by ISPs and law enforcement agencies to identify email harvesting/spammers.

Best Practices: Maintain list hygiene with hard and soft bounces. Bounce notices can provide invaluable information about how Outlook (or any provider) is treating your messages. It is critically important that you keep spam trap rates below 0.01% to avoid reputation issues.

5. Properly Configure Your Sending Infrastructure and Content – Microsoft looks for well set up infrastructure and aligned content as an indicator of a good sender. Microsoft also applies a proprietary content filter called SmartScreen. SmartScreen learns from data provided regarding known phishing threats as well as from Microsoft customers to determine what characterizes good mail and unwelcome mail. Filtering is accomplished by probability-based algorithms used to distinguish between legitimate e-mail and spam.

Best Practices: Always use valid, reputable URLs. Avoid using IP addresses in the URL. Publish your Sender Policy Framework (SPF) records. Focus on content, as well as URLs and HTML elements.

6. Sending Frequency and Consistency – Sending from the same IP address(es) with consistent volumes and frequencies month over month is ideal. Spammers tend to “pop up” on an IP and disappear. Infrequent senders who send large volumes once a month or quarterly can be an indicator of a spammer or a compromised server.

Best Practices: Be consistent.  Segment your sends. Prioritize sending genuinely wanted content to a smaller number of engaged subscribers over sending generic content to your entire list. Include your call to action early in your content so subscribers will see it quickly as they scan your message.  Avoid link shorteners like and align your links with your content.  Personalize your content to your subscribers’ interest.  Don’t send the same content to your entire list, but instead but segment and personalize using dynamic content.

The Golden Rule for Hotmail/Outlook Deliverability

Overall, Microsoft has incorporated content filtering with authentication and reputation for a combined “trustworthy” score with which it determines how to handle messages and determine Hotmail/Outlook deliverability.  So the simple answer is to follow best practices consistently. Send to only subscribers the content that they expect, when they expect it. That’s the golden rule of email deliverability to Outlook or any ISP.

For more information about Hotmail/Outlook deliverability straight from the source, visit the Microsoft postmaster page.


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When senders and receivers work together, we all win.

Twitter, Google, Microsoft, AOL and Comcast?

That’s right. We promised that Interact 2013 – The Digital Messaging Industry Conference, would be bigger and better – and we’re making good on that.

The five online titans form the A-list ISP panel that will be spearheading the discussion on Preserving the Email Ecosystem. They’ll be discussing sending best practices and acceptance policies, as well as ways senders and receivers can cooperate to keep the email ecosystem clean and spammers at bay.

Josh Aberant from Twitter will be moderating this event, while the panelist line-up includes:

John Scarrow – Microsoft
Lachian Maxwell – AOL
Olga Gavrylyako – Google
Severin Walker – Comcast

If you’ve ever had burning questions about email deliverability, this is the forum to get those concerns addressed by the gatekeepers themselves.

When it comes to actionable takeaways to increase email deliverability, there’s no better way to learn. Aside from the A-list panel, Interact 2013 features two separate tracks: Digital Messaging Best Practices & Interact Bootcamp, where you’ll hear from email experts – both senders and receivers – from Oracle Eloqua, Groupon, Alchemy Worx, Acxiom, Barclays, OTA, XING and more.

I just came across one of Microsoft’s many visions of the future. Being a gadget guy at heart and a lover of cool interfaces that make things easy, I thought this was a pretty compelling vision. (Though I did wonder why people of the future often look so spacey!) (more…)