A follow-up email nobody had looked at in years, and what happened when we changed only its subject line.
A vehicle transport business we look after sends a follow-up email to everyone who asks for a quote.
About 500 a day. It goes out automatically, it carries a link to book, and for years its subject line read like a receipt:
Accurate, official, and easy to leave unopened, because it looks like something you already have.
On 6 October we changed the subject line and nothing else. Same email, same link, same price, same timing. The new one asks a question, and it names the customer's own car:
It reads like a person checking in, which is what the email was always for.
We took every follow-up sent in the four weeks before the change (14,680 of them) and every one sent in the first six days after it (3,018), and followed each email for seven days after it went out. Was it opened, was the booking link clicked, and did that customer book?
Then we checked the thing that most often fools a before-and-after comparison: the season. Across all quotes, not just the ones that got this email, bookings within a week actually went down over the same days, from 4.4 to 3.7 per 100. So whatever moved the follow-up numbers, it was not a busy patch.
The clicks are the clear result. That jump is far too big to be chance: nearly twice as many people went from the email to the booking page.
Bookings are an early sign, not proof. They went the right way while bookings overall went the wrong way, but six days of data is not enough to be sure. We are measuring again in a fortnight, and we will say what we find either way.
Opens went up too, though we trust that figure least. Some mail apps open every email automatically, so open counts run high on both sides.
No new system, no new software, no extra emails. The follow-up had been going out for years, and nobody had looked at its subject line, because it worked well enough and nothing about it was broken.
In a business that runs on enquiries, a lot of the money is not in the big systems. It is in the small automatic things that run thousands of times a month and that nobody has opened in years: the follow-up email, the confirmation text, the quote page on a phone.
Change one thing. Measure it honestly, against something that did not change. Then say plainly which part is proven and which part is still a hunch.
Here the clicks are proven. The bookings are a hunch with good evidence behind it, and we will know more in early November.
The client is not named. "Toyota Hilux" and "Ref# 123456" are examples: the real email fills in each customer's own car and quote number. Every figure above is taken from the business's own records.