Which works best? Specific or general subject lines?

When to use specific subject lines (and when not)

The more people open your email, the better. So your subject line should go for maximum opens, right? Probably not, actually. Here's why...

First, take a look at your email list. Don't they look happy?

You're going to send out a standalone promotion for Widgets. The red people may want to buy one. The blue ones have no interest.

(The orange one is a competitor monitoring your emails. And the green one is an email marketer collecting creative for her swipe file.)

Should you use a specific or more general, inclusive subject line? Here's what others say:

Claude C. Hopkins wrote in Scientific Advertising in 1923 (yes, 1923!):

"Address the people you seek, and them only"

In their seminal 2008 study of subject line length Alchemy Worx concluded (my emphasis):

"Getting more people for whom the message is relevant to open the email requires a subject line that is specific and detailed..."

Tim Watson, who has conducted a lot of subject line research, recently stated (again, my emphasis):

"The subject line is used by customers to self-qualify, if the subject line does not accurately qualify the right people then customers who might have taken action do not open and conversely some open only to find it’s not the right message for them."

So it's not about getting more people to open, it's about getting the right people to open - the people most likely to actually act on the message. And that usually means a specific, clear subject line.

The concept seems logical. Going back to your list, say you send out a very specific subject line featuring the product offer. Something like:

Today only - save 10% on Widgets"

Here's who opens the email:

That's about 20%. Or you could send out a more general subject line that creates more curiosity and interest. Something like:

Today only - special offer inside!

Here's who opens the email: Much better - the open rate is now 50%. Hurrah!

But wait...here's who actually clicks and purchases after seeing the specific subject line: That's a 20% CTR measured on sent email and 10 sales.

Now here's who actually clicks and purchases after seeing the general subject line:

That's an 8% CTR measured on sent email and 4 sales.

And that's why you should not base subject line tests on opens, but on sales or whatever your actual campaign goal is.

The general subject line gets more people to open, but many of those people were just curious or intrigued and discovered the actual offer was not relevant to them. Unfortunately, not everyone who might buy the actual product was intrigued enough to open, either.

The specific subject line attracts the attention of the prospective buyers more effectively, leading to more sales. The fewer opens does not matter, because those who don't open were never going to buy anyway.

Like all things email, it's not quite as clear cut as our rather simplistic example suggests. But the point stands: specific tends to beat general.

Now, of course, there are exceptions, which is another reason why subject line testing is so important. For example:

1. If your email features too many items or topics to describe in the subject line, you may have to fall back on enticing, general approaches. Or you can combine specific and general approaches, such as "Huge flight sale - Paris, London, Frankfurt..."

2. If your email content or offer has very broad appeal among recipients, maximizing opens might indeed maximize clicks and further actions. The more targeted the audience, the more creative freedom you have.

A similar scenario is where you're not looking to drive specific actions, but simply to get people engaging with your email for branding, awareness or similar purposes. Don't lose sight of the fact that long-term success means recipients still need some sort of reward for that open, or they won't bother next time.

3. If you can offer those not interested in the main offer or content other alternatives via sidebars, secondary links, navigational menus etc. The net results may then justify a more inclusive subject line.

4. If a mixture can help keep people engaged with your emails in the long-term. A stream of general, teaser, intriguing subject lines can end up disappointing people if the content or offer itself isn't of value. It can train them to distrust or ignore future emails.

Equally, a stream of very specific subject lines can train people for whom the right offer has not yet come to eventually switch off from your emails. So it can often help to mix it up a little.

This is particularly plausible for emails that deliver more than just the functional value of the offer or content. Is there value for the recipient in the email itself, through the personality of the copy, the creativity of the design, humor, the impact of the images and similar?

5. If people have become desensitized to the style used in your specific subject lines. An alternative approach (for example, for inactive subscribers) might help rekindle interest.

6. If how people interact with emails comes to play a key role in defining your position in the inbox. I've seen conflicting views on whether higher opens, for example, lead to a better sender reputation or priority inbox placement at certain ISPs. For now, I'm not convinced it should be a meaningful consideration in planning subject lines, but I keep an open mind.

What's your experience with specific versus general subject lines?