Email Sender and Domain Reputation

Help: I’m Blocked at

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Now and then I find myself daydreaming about football…

Not just being at the game, but playing the game, professionally. A little off topic, right? Well sort of, but stay with me. In my daydream, I am the star running back. The stands are packed, the fans are unhinged, and our team is down by three points. It’s late in the game; the passing game isn’t doing so well, so it’s all up to me. As the running back, it’s my job is to take the hand-off from the quarterback and run in a touchdown. This means counting on my team to block defenders and find the openings to score–which in my daydream, happens a lot. After each touchdown the crowd erupts, my team is elated, and everything is great! And as my misty, water-colored daydream starts to close, the cheers die down, and reality creeps back i

I look around and realize that I’m not a professional football player. I’m an email marketer. The only touchdown I’m trying to score is getting my email campaign into my customer’s inbox and, the only blocks I’m getting are from mailbox providers. Unless you’re a running back, there’s never a good block. So, I’ve put together a list of steps you can follow to avoid having your mail blocked at

Before we get started, don’t just take my word for it.’s postmaster page does a great job of outlining steps to avoid getting blocked.

Step 1: Check your bounce logs/non-delivery reports (NDRs)
Some mailbox providers including, provide senders with bounce logs. These logs will include an SMTP error code with a block. This includes a specific error code with the NDR (i.e., 421 RP-001, 550 SC-004, etc). NDRs have different translations. For a breakdown of’s SMTP error codes, click here and scroll to the end of the page.

Step 2: Follow’s policies, practices, and guidelines

  • Confirm DNS: The sending IP address of your mail server should have a valid reverse DNS record using a fully qualified domain name. This will ensure your domain won’t be blocked for appearing to use a dynamic IP address.
  • Authentication: only validates inbound mail using sender policy framework (SPF) and sender ID authentication.
  • Unsubscribe link: Provide an easy-to-find button or link to unsubscribe from individual or all lists for subscribers.
  • Connection settings: Avoid opening more than 500 simultaneous connections to inbound mail servers. More than 500 will result in messages being throttled. Click here for more detail from

Step 3: Maintain your sender reputation
Sending history, subscriber complaints, and list quality are important measures and other major mailbox providers look at to decide whether or not an email should be blocked or sent to the junk folder.

  • Sign up for Microsoft’s Smart Network Data Services (SNDS): This valuable tool provides data to help monitor your IP address activity for SNDS helps identify campaigns resulting in excessive complaints and spam trap hits. This tool identifies the root cause(s) of issues and takes the appropriate action to correct the problem.
  • Reduce complaints: Now that you’re signed up for SNDS, you need to set up your Junk Email Reporting Program (JMRP)’s free feedback loop that monitors and mitigates complaints. But don’t just remove the complaints from your list. Use the feedback loop data to help you identify why they complained in the first place. Keep track of campaigns that experience a high rate of complaints and use them to troubleshoot potential problems. Consider engagement, content relevance, list acquisition sources, and the age and activity of the data generating complaints. Use this data to make strategic adjustments to your program.
  • Symantec’s Brightmail anti-spam filtering: utilizes Brightmail’s anti-spam content filter to decide where to place mail. Brightmail’s technology protects subscribers from junk email before it reaches the inbox. If you happen to have a high percentage of mail considered suspicious, your IP address could be bulked or blocked. You can check your Brightmail IP address reputation and request block removal here.
  • Remove invalid addresses: Manage your list by removing invalid subscriber accounts (unknown users) and unengaged subscribers. Don’t be tempted to keep a longer list. If your list includes unengaged users, invalid addresses, or even questionably acquired lists,’s filtering methods will easily detect this.
  • Send from IP addresses with a positive reputation: Microsoft wants you to deploy your mail from IP addresses with an established sender reputation. A new IP address without historic volume will not carry a positive reputation. As a result, mail sent from new IP addresses is usually filtered into the bulk folder until a positive reputation is observed. Take a look at this recent blog for details on IP address reputation.
  • Verify your IP address reputation: Regularly check your IP address reputation and the various factors causing any decline via Return Path research shows the higher your sender score, the better your chances of reaching the inbox. This blog outlines the importance of checking your sender score.

Step 4: Subscriber Engagement
Subscriber engagement impacts whether your email reaches inbox’s or junk folders. Microsoft looks at the following areas of engagement to decide whether or not to send email to the inbox or spam:

  • Messages opened/engaged
  • Whitelisted messages
  • Messages deleted without being read
  • Messages replied to
  • Frequency of receiving and reading a message from a source

While you may not have insight into these metrics, you should track opens, clicks, conversions, web activity, etc. on your end. If your subscribers don’t register any activity based on your internal metrics, chances are they aren’t performing for Microsoft either.

Help subscribers stay engaged by setting the proper expectations up front regarding the type and frequency of email the subscriber will receive. Deliver on what you promised with email that is relevant to them and that they can easily recognize is coming from you.

Step 5: Get certified with Return Path uses Return Path’s certified whitelist. This is one way to avoid being marked as an “unknown sender” by Having a third-party like Return Path accredit your sending practices means can deliver your email to the inbox with images enabled. Acceptance into the program positively impacts delivery and in most cases results in a lift in delivery.

With all that in mind, you can daydream away—knowing your Outlook subscribers’ email is landing in the inbox. Now, the only blocks you should see are on the field.