Best Subject Line Tester Tools That Will Help You Boost Your Email Open Rate

At this point, everyone knows how important email marketing campaigns are. They are a sure way of increasing traffic to your website, generating new leads, and in turn, gaining new customers. However, they only work if those potential customers are actually opening your emails and clicking through them. There really isn’t any point to them if they are straight-up ignored by people who receive them.

If you want your #emails to be interesting and make people want to engage with them, you have to write email subject lines that are bound to grab their attention.

Different email campaigns with different goals need to have unique content that simply can’t be ignored. Unfortunately, that isn’t always possible. Sometimes you are just not creative enough, so you mess up your email subject lines and end up with an email that hasn’t been opened by many recipients.

That’s exactly why subject line tester tools exist; to help you generate better results. 

1. SimilarMail


SimilarMail is an email archive and analytics service that will help you optimize your email open rate and give you insight into the email marketing campaigns of your competitors. With this tool, a low click-through rate is a thing of the past.

SimilarMail gives you a collection of more than 4 million email designs from 40.000 leading brands. So with everything they are offering, it’s going to be impossible to have an email with a bad open rate.

It’s important to know what works these days, what are the current trends, and what potential customers are interested in. With SimilarMail, you can gain knowledge of those trends as well as get design inspiration from brands that are at the top of the game.

You can access newsletter archives of major brands to get a glimpse into what worked for them and how you can incorporate that into your own campaigns. 

SimilarMail popular brands and domains

The data and insights that will be given to you, which include things like what time of day or week is best for sending marketing campaign emails, is what you need to increase open rates, click-through rates, and conversion rates.

With this information, you won’t make the mistake of sending out an email when everybody is sleeping. Furthermore, you will improve customer experience through things such as customized content as well as mobile-optimized content.

SimilarMail analytics

Another very important feature that SimilarMail is going to offer you is tracking content and trends for holidays such as Valentine’s Day, Black Friday, Christmas, and so on. Planing your marketing calendar and knowing how to use certain keywords is the key to success when it comes to email marketing campaigns.

On top of all that, you can even get insight into your competitors’ marketing tactics.

SimilarMail email strategies

By using SimilarMail’s content and subject line analysis features, you will learn what the best content and subject line strategies are and how you can implement them into your work.

The SubjectAI open rate prediction technology will, you guessed it, predict your email open rate and identify the best subject lines. Using such technology will tell you what works best and what could help you out. 

With SimilarMail, you can even discover what marketing automation technologies work best and then use the right platforms and services for your business.

2. TestSubject


TestSubject is the perfect tool for creating mobile-friendly email subject lines and testing how they will actually look on mobile devices. Nowadays, we are on our phones most of the time, so it’s important to optimize emails and other content for those devices.

With TestSubject, you can test how the sender’s name and subject line will look like on a mobile device. Often, those are truncated, which results in text that looks funny and unprofessional. 

To test how your subject lines will look, you just have to copy and paste them, and you will get a preview. This allows you to make changes if needed before actually sending out the email. You can also see the preview on different devices, such as iPhone and Samsung.

3. Mizy


Mizy is another AI-powered tool that can grade your subject line based on more than a million email campaigns and will work on improving your open rates.

Mizy will access a database of other emails and see their click-through and open rates. By gathering data and providing insight into other successful email campaigns, it can test your subject line and improve it.

When you enter your subject line, Mizy will give you a rating and tips on how to make it even better. The score provided is not based on benchmarks, fake best practices, or old case studies. Instead, it is based on the results of real past campaigns.

4. IsNotSpam


Aside from people not opening your emails, another problem is your emails going into the spam folder. Emails that go into the spam folder have even less of a chance of being opened because they are most likely being deleted immediately. Nobody wants to catch a virus from a suspicious email.

To prevent your emails from being detected as spam, you should test them before sending them to make sure everything is in order.

IsNotSpam is typically used to test the content of an email, but it is good for testing the subject line as well. It performs five tests, including SPF Check, Sender-ID Check, DomainKeys Check, DKIM Check, and SpamAssassin Check. 

To perform a test, you just have to copy the email address provided on the tool’s website and send your email to that address. Lastly, you just click the “View Your Report “button, and you’re done.

Final Thoughts

One of the most important marketing strategies is email campaigns. They can increase traffic to your website, generate new leads, engage existing customers as well as attract new ones. However, a problem arises when your emails are being ignored and don’t serve their purpose.

Often, emails are not opened because their subject lines are just not interesting or good enough. Thankfully, there are many tools you can use to test your subject lines and see how impactful they are.

Using SimilarMail or other tools mentioned above is your best bet and will for sure help you have better open and click-through rates.