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Make It to the Inbox With Litmus Spam Testing


If you’re like the nearly 60% of email marketing pros who responded to our 2021 State of Email survey, you invest more than two weeks into your email production cycles. But did you know 16% of all emails never make it into the inbox?

While email deliverability can feel like a bit of a mystery at times, you don’t have to cross your fingers and hope that your messages end up where you intend. With Litmus Spam Testing, you can identify and fix issues that might otherwise land your emails in spam—long before you hit send.

Read on to learn more about why spam tests are so important, what they can help you identify, and how to conduct them.

What is Litmus Spam Testing?

Litmus Spam Testing scans your emails against 25+ different tests, identifying any issues that could prevent you from landing in the inbox. Best of all, it provides actionable advice for how you can fix them, before you hit send.

Know if you’re blocklisted

There are generally two types of blocklists—one is at the internet protocol (IP) level, and the other at the domain level (such as and

Blocklists are intended to help identify IP addresses and domains thought to send spam emails. As an email user, blocklisting filters out emails that you don’t want to receive so you don’t get bombarded with junk messages. But as an email marketer, being on a blocklist may mean your emails won’t make it to your subscribers.

Here are some events that may land you on a blocklist:

  • You are one of many “senders” using your email service provider’s (ESP) shared IPs
  • Recipients mark your email as spam instead of unsubscribing
  • You are mailing to outdated lists with email addresses that are incorrect or no longer operable
  •  A number of subscribers stop opening, clicking through and engaging with your messages
  • You’ve hit a spam trap

Blocklisting can happen due to any number of factors that you can (and should) work to prevent—but it’s important to know that not all have the same impact on deliverability.

Litmus Spam Testing checks your IP addresses and domain names against common blocklists, indicates whether you appear on them, and helps you prioritize your response with a high or low  impact flag that indicates how impactful the listing could be for your email delivery.

Ensure infrastructure is set up for success

Confirming that you’ve properly authenticated any domain you use is one the most basic steps you can take to improve the chances that your email will make it where you intend. Our spam testing tool makes it easy to validate that your DomainKeys Identified Mail (DKIM), Sender Policy Framework (SPF), and Domain-based Message Authentication, Reporting & Conformance (DMARC) records are functioning correctly.

Pre-screen your messages across major spam filters

Running an email spam test with Litmus is simple. Once you’re logged in to your Litmus Plus account or Enterprise plan, you can select “start a new spam test” and copy the list of seed addresses (unique to you, and the test). Then, send your email from your ESP to those seed addresses. Your email testing results will populate in Litmus in less than ten minutes.

Or, you can use ESP sync to choose an email from your drafts to send into Litmus when you start a new spam test.

Get actual advice to improve your email

Once your spam test is complete, you’ll get a visual overview of the results that returned an issue—and a ranking of how critical that issue is to your campaign success. You can also choose to view an individual test by clicking on the corresponding square.

In addition, Litmus Spam Testing offers best practices to help you prioritize technical issues you should address before you send, and tips and tricks for more minor issues that could impact inbox placement (but won’t necessarily derail your email campaign) and how to resolve them.

What spam filters does Litmus’ tool test against?

A lot of factors can affect your email deliverability. Our spam test gives you insight into what might get your email marked as junk. Here are the main filters it tests against.

Email authentication

Email authentication looks at the source of an email to see if it’s valid. Also called domain authentication or validation, email authentication helps prevent spoofing and phishing scams (like emails meant to look like they come from Amazon or your bank—but don’t).

Here are some of the authentications our email spam test considers:

  • DomainKeys Identified Mail (DKIM). Shows that your email is associated with your domain. In turn, this essentially allows your organization to claim responsibility for your email.
  • Domain-based Message Authentication, Reporting & Conformance (DMARC). Meant to combat phishing and helps you identify if a sender is attempting to impersonate you.
  • List-Unsubscribe. An optional email header that allows for an easy and consistent unsubscribe action.
  • Sender Policy Framework (SPF). Allows a domain owner to indicate multiple IP addresses or domains that can send mail on their behalf via a DNS TXT entry.
  • TLS. STARTTLS, or Opportunistic TLS. Gives senders the ability to encrypt email in transit.

Placement filters 

Placement filters evaluate emails against a set of criteria—which changes over time. These filters are looking at a combination of engagement, reputation, authentication, formatting, and content and word triggers. Litmus Spam Testing checks your email against the following placement filters:

  • AOL Mail
  • Gmail
  • GMX
  • GoDaddy
  • G Suite
  • Office 365
  • Outlook
  • Yahoo
  • Yandex

Score filters

These scores show you the likelihood a spam filter tool will catch your email and put it in someone’s spam inbox.

  • Barracuda. Barracuda Essentials for Email Security is a sophisticated anti-spam and email analysis tool often used by large organizations.
  • Microsoft Exchange Online Protection. Uses a built-in malware and spam filter to evaluate and score email.
  • Broadcom Messaging Security. An antivirus and spam analysis tool, used by organizations to protect corporate email.
  • Outlook Desktop. Outlook comes with a built-in junk email filter that “learns” spam emails over time.
  • SpamAssassin. An open source spam filter that analyzes email headers and body text by using text analysis, bayesian filtering, DNS blocklists, and collaborative filtering databases.

Blocklist filters 

A blocklist is a real-time collection of senders thought to be sources of spam or other types of email abuse. Blocklist providers may use a combination of spam traps, spam complaints, and other proprietary data sources as criteria for adding a sender to a blocklist. Inbox providers often maintain their own proprietary blocklists, using them in combination with independent, third-party blocklists.

Why is email spam testing important?

You can’t look at an email and know if it will land in a spam folder 

Avoiding the spam folder requires so much more than not using certain words or symbols in your email subject lines. There are so many issues that could potentially land you in spam that you can’t predict as possible issues manually—from blocklists to email content to varying scores and weights that a spam filter uses to decide whether an email is spam.

In fact, on the heels of an email filtering bill alleging that political email communications are unfairly put into spam, Google is now in talks with lawmakers to explore a pilot program that would “provide more transparency into email deliverability, while still letting users protect their inboxes by unsubscribing or labeling emails as spam.”

Emails in the spam folder waste your  opportunity  

Nearly 80% of email marketers who responded to our 2021 State of Email report ranked email among their top three most important marketing channels. If your emails are landing in the spam folder, you’ve missed out on all that opportunity!

Protect your email deliverability and sender reputation

Spam testing can help you spot—and correct—issues before you send, protecting your email deliverability and sender reputation.

Maximize your chances of engaging subscribers

You’re sending emails to engage subscribers with some goal in mind. But the ways in which they engage with your messages also shows inbox providers people actually want to engage with your messages. When they know you’re a trusted sender, inbox providers are more likely to put your messages where you want them—the inbox!

How do you interpret the spam test results?

Once your spam test has run, you’ll see a high-level summary of your results. From here, you can drill deeper into issues that were uncovered.

Litmus Spam Testing results

  • If a filter shows a green square or says “Passed”, you’re good to go!
  • If a filter shows a yellow square or is marked as a minor issue, you can still move forward with your send. However, it’s a good idea to review what the filter flagged so you can monitor the issue. Unaddressed issues can become critical over time.
  • If a filter shows a red square or is marked as a critical issue, do not hit send until you resolve the issues flagged. When you click to review the results of that filter, you’ll see a sidebar with recommended action steps. You may want to involve the person that manages your email infrastructure to help you figure out  issues to resolve before you continue sending emails.

How to get started with Litmus Spam Testing

If you already have a Litmus Plus or Enterprise account, log in and navigate to the Test tab. From there, select “View and create spam tests” in the slider menu.

Litmus testing tools and preview settings

Here, you’ll be able to start a new spam test or see the results of a recent one.

Run spam tests regularly

Email clients update every 1.2 days on average, and you may be completely unaware of the changes. In the same way, the algorithms for spam filters update regularly. And sometimes, your IT or dev team may change an IP address without realizing it impacts email. At any rate—an email spam test helps keep you in the know!

Landing in the junk folder is more than just bad for your marketing campaigns and reputation. It cost you in the  form of wasted resources, lost revenue and missed opportunities to connect with your subscribers. In some cases, it may even require hiring a company to fix your sender reputation.

Make it a best practice as part of your email workflows to run spam tests regularly, and keep your email campaigns alive and well!

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Try Spam Testing free for 7 days

New to Litmus? Sign up for a trial of Litmus Plus and try Spam Testing free for 7 days. You’ll also get access to Litmus Test for a guided check of all critical elements in your email, Email Previews in all popular clients and devices, data insights with Email Analytics, and more.


Originally published on June 7, 2017, by Bettina Specht. Last updated July 15, 2022.