If you have been searching for the best cold email subject lines for your outbound campaigns, you’ve been doing it all wrong. I know that sounds counterintuitive, but please hear me out.

Cold email is getting tougher by the day, and it is harder to get into the inbox and even harder to get a response from prospects. In such a competitive marketing channel, it is natural for people to search for ways to stand out and get better responses. I hate to break it to you, but there isn’t any magic potion that is going to solve that problem for you.

your prospect's inbox

Instead, you need an analytical approach to testing your cold email campaigns and find what works the best. That’s what the “best subject line” crowd doesn’t understand. There is no get-rich-quick scheme that works for your campaigns.

The same applies to subject lines.

How do you conduct meaningful tests? You start with your gut instincts and market trends and then tweak your subject lines depending on your outbound campaign performance.

In this blog, I share how to A/B test your cold email subject lines to improve your overall campaign performance.

Before that, let’s look at why the best subject lines don’t exist.

Why best subject lines don’t exist?

You might see some results if you use something from an article that claims to have the best subject lines. But sooner or later, you will see that your open and reply rates are plummeting.

Here are a few reasons why the mythical subject lines don’t exist.

Some subject lines are overused.

The top two search results for “best cold email subject lines” include an article from Brafton and another from Hubspot. HubSpot gets a monthly traffic of 2.7k from this page, and Brafton receives around 1000 visitors a month from its page.

Now, that’s 3.7k people visiting these pages, and a significant percentage of these folks are using the subject lines listed on these pages. The average business professional receives 100+ business emails a day. You can imagine how frequently a prospect receives similar-sounding messages with identical subject lines.

hubspot's entry for best cold email subject lines

brafton's entry for best cold email subject lines

Subject lines like “quick question”, “, question?”, “, thoughts?” have been overused in the last two years. So much so that they immediately raise your prospect’s mental spam filters.

So, when you use a subject line from such search results, you will probably commit the same mistake and get ignored. Here’s the simple reason, your email has no pattern interrupt, and your prospects have been trained by cold emailers around the world to ignore such messages.

Subject lines are personal.

Another reason why “best subject lines” don’t exist is because there can’t be a one-size-fits-all all when it comes to cold emails. Cold emails are a medium of connecting with potential buyers. Buyers have business problems to solve, so when you come up with something generic you found on the internet, you are ignored by them.

You might get a few responses from unsuspecting prospects, but your campaigns won’t be a success. The least you need to do is keep prospects with similar persona and account traits and with similar challenges in the same campaign. This way you can keep your subject lines personal and relevant.

How to search for the best subject line for your cold emails?

Searching for the best subject lines means that you need to have a continuous process to find out what works at a given time for a target persona and ICP. You might have to go through multiple iterations before you find something optimum.

For a guideline, any subject line that generates 60%+ open rates and 5%+ reply rates can be considered high-performing.

Here are a few ways in which you can keep looking.

Use A/B testing.

A/B testing for cold email copy is standard, and most sales reps and cold emails run A/B tests. Angles could include testing the CTA, the value proposition, and the introduction line. Each one of them gets you closer to higher reply rates.

But you can’t get replies to your emails if they aren’t opened. Thus, you need to A/B test your subject lines with the email content.

Having a weekly routine of including a test subject line with what’s already working can be a great way to benchmark performance while figuring out what’s next.

Use personalization.

Personalization can also lead to your optimum subject line and much faster. With personalization, you can run multiple subject lines simultaneously. And personalization comes in two levels for subject lines -

  1. Person level - Here you are personalizing the subject based on the individual’s needs. The parameters could include their business needs, their role’s challenges/goals, or their professional journey. This way you can figure out whether people in your buyer persona are receptive to “person-level” personalization.
  2. Segment/Persona level - In this method, you club together similar roles or people in similar industries/target accounts. And then personalize your subject lines to those parameters. The level of personalization is lower but your coverage is greater in this method. Thus you can test the performance of the subject lines faster since the sample size is greater than the “person level.”

How to run A/B tests for subject lines in cold emails?

Most cold email outreach software doesn’t have a dedicated analytics dashboard for A/B testing subject lines. But you can implement workarounds to get to know which subjects work better than others.

Use split testing in your email software

For tools like Smarltead, Reply.io, and others you can create different variations of email copy. In these copies, you can also include different subject lines to test performance against each other.

If you want to test the performance of subject lines while keeping the email copies the same, do this. Create multiple variations within your email outreach software and keep the email copy the same. Just use different subject lines for each of your variations.

You can check open rate performance in your analytics dashboard and get a quick overview of what’s working and what isn’t.

Here’s how it looks in Smartlead.

smartlead subject line testing

Use spintax for the subject lines

You can also include an element of gut feeling in your testing. This works well if your outreach numbers and sending volume are low. Let’s say you send just 100-200 new emails every week. In that case, the numbers are too low to do an A/B test for subject lines.

Instead, you can include subject lines addressing different outreach angles using Spintax. And when you see that certain subject lines tend to get higher replies than the rest, you will have nailed down your ideal subject line.

Create a framework for measuring performance.

For all of your subject lines, you should have a measurement process. Ideally, you need to know overall open rates and reply rates for your subject lines. If you want to go deeper, you can also include the deal conversion metrics in your measurement process.

You should be able to answer the following questions from your metrics -

  1. Which subject lines give me above-average open rates?
  2. Which subject lines give me above-average reply rates?
  3. Which subject lines have the highest deal conversion rate?

Mapping metrics throughout the process informs your future tests and improves overall conversions.

I hope you now believe, that the best subject line for cold emails doesn’t exist. It is just what you make out of your ideas.