I Used ChatGPT to Write Email Subject Lines: Here’s What I Found


The professional world has become oversaturated with blogs, LinkedIn posts, Tweets and podcasts about the rise of ChatGPT. It makes sense! ChatGPT has forever changed the way we write and generate ideas.

Do I think that ChatGPT is going to replace writers and creatives the same way the internal combustion engine replaced horses? No. Not at all … at least not in the near future.

It’s best to look at ChatGPT and other similar AI-generated technology to jumpstart your writing processes and save you time. You can think of it as your own personal scribe and virtual assistant, not as a young prodigy who’s going to take your job and render you useless.

Case in point: email subject lines. Instead of sitting down at my computer and writing out 10 subject lines, I can offload that task to ChatGPT!

Asking ChatGPT to write 10 subject lines

AdFarm had a client that needed to send an email to their list about the importance of even fertilizer distribution. Inside the email were terrific, value-packed blogs and videos that educated the farmer on how even fertilizer distribution will help their farming operation.

So, I opened up a new project in ChatGPT and asked it:

Can you write 10 email subject lines for me on the importance of an even distribution of fertilizer on a farmer’s field?

To which ChatGPT responded:

  1. Boost Your Crop Yield with Proper Fertilizer Distribution
  2. Don’t Let Uneven Fertilizer Distribution Hurt Your Harvest
  3. Why Even Fertilizer Distribution is Critical for Crop Health
  4. Maximize Your Field’s Potential with Even Fertilizer Application
  5. The Key to Successful Farming: Even Fertilizer Distribution
  6. Prevent Crop Losses with Proper Fertilizer Placement
  7. Get the Most Out of Your Fertilizer Investment with Even Distribution
  8. How Uneven Fertilizer Application Can Affect Your Bottom Line
  9. Don’t Let Poor Fertilizer Distribution Negatively Impact Your Crop Quality
  10. The Importance of Even Fertilizer Distribution for Sustainable Farming

The AI generated 10 subject lines in 15 seconds. That task would normally take me 15 minutes.

Even though that was a great start, I wasn’t sure which of the 10 would perform best. While ChatGPT can’t run A/B tests on email subject lines (obviously), it can give me reasons why some of these may outperform others.

Which one do you think will perform the best?

And ChatGPT responded:

It’s difficult to predict which subject line will perform the best as it depends on various factors, such as the target audience, the purpose of the email, and the sender’s reputation. However, subject lines that highlight the benefits of even fertilizer distribution, such as “Boost Your Crop Yield with Proper Fertilizer Distribution” or “Maximize Your Field’s Potential with Even Fertilizer Application,” may perform well as they emphasize how even fertilizer distribution can positively impact the reader’s farming outcomes. Additionally, subject lines that create a sense of urgency or emphasize the negative consequences of poor fertilizer distribution, such as “Don’t Let Uneven Fertilizer Distribution Hurt Your Harvest” or “Prevent Crop Losses with Proper Fertilizer Placement,” may also be effective in capturing the reader’s attention.

Brilliant! We’ve narrowed it down to four subject lines, two playing off the strong desire for farmers to increase crop yield (that means they make more money) and two that play off of their fear of a bad harvest (that means they make less money).

Always be testing

Now is the part of the process where you, as an email marketer, would pit the two subject lines against one another. For the sake of moving this example along, I will pick two for you. I like the positive association of the word “maximize” and the negative association of the word “hurt,” so we’ll go with those.

I’d then run an A/B split test on those two subject lines:

  1. Maximize Your Field’s Potential with Even Fertilizer Application
  2. Don’t Let Uneven Fertilizer Distribution Hurt Your Harvest

In Mailchimp (the email marketing service this client uses), I’d send 10% of the audience subject line 1 and 10% of the audience subject line 2. I’d then span that test over 4-6 hours. Once a winner was picked based on the higher open rate, the remaining 80% of the audience would receive the winning subject line.

If your sample size is big enough and the disparity between the two subject lines is great enough, you then have feedback for your clients (or your business) about what moves the needle more: optimism or fear?

These micro decisions can impact your macro strategy on a long enough timeline with enough data points to signify a clear pattern.

By outsourcing some of these decisions to ChatGPT, you are also removing your bias from the equation. Yes, ChatGPT is biased as well – after all, it’s programmed by humans – but in this example, there is little reason for it to be outwardly biased.

Don’t fear the tech … embrace it!

Source: Twitter / DocumentingBTC

I get a kick watching YouTube videos of old news broadcasts where the hosts talk about the internet as a fad and debate its usefulness. The early ‘90s were full of these hot takes just as today, everyone and their grandma has an opinion on the future of AI-generated words, images and videos.

This technology isn’t going anywhere – in fact, it’s going to grow at breakneck speeds over the next decade. This is going to present many obstacles for everyone from teachers to national security apparatuses as we try to discern what is “real” in a world where people and robots can produce millions of hours of content in seconds.


Learn how to work with technology like ChatGPT. Those that do will hold the power of content generation going into the future. They will be the new age composers at the front of a digital symphony, expertly telling each instrument what to play, how to play it and when.

Andrew Donovan

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