Subject lines without the tricks

Subject line advice is mostly a list of tricks, and the tricks have a cost that is never counted: they work once, they damage the sender, and in the United States a subject line that misrepresents the contents is specifically unlawful rather than merely poor practice.

The one rule with legal weight

The FTC requires that the subject line reflect the content of the message, and that header information including the from address be accurate and identify who sent it. Those are not guidelines. Australia's regulator similarly requires accurate identification of the sending business, and has pursued senders for labelling marketing as service messages.

So re: and fwd: on a message that is neither, a from name that is a person who does not exist, and a subject promising something the body does not contain, are the wrong side of a line rather than merely cheap.

What actually gets opened by the right people

The distinction matters. Getting opened is easy; getting opened by people who then read, reply and stay is the thing. Curiosity gaps and fake urgency do the first and damage the second.

• Say what is inside. The five checks before you launch. Prices going up on the first. The thing that broke last week. Specific beats clever, consistently.
• Use the reader's own words. If customers say stock count rather than inventory management, say stock count.
• Keep it short enough to survive a phone, where a long subject is cut and the end of it is where people put the interesting part.
• Make the from name a constant. Recognition does more for opens than any wording, and changing it between sends throws that away.
• Let the preview text do work. It is the second line in most inboxes and most senders leave it to repeat the first line of the message.

Testing, at a small size

Split testing subject lines needs more recipients than most small lists have to produce a result that is not noise. On a list of a few hundred, a difference of a few opens is chance, and treating it as a finding leads to a year of confident nonsense.

What works instead: pick a style, use it consistently for a few months, and watch the direction of unsubscribes and replies. That is slower and it is the only version of the question a small list can actually answer.

The things to stop doing

• False urgency. Deadlines that do not exist train people to ignore the ones that do.
• Re: and fwd: on messages that are neither.
• A first name in the subject for no reason, which reads as automation rather than familiarity.
• All capitals and rows of exclamation marks, which are the oldest filter signals there are.
• Promising a discount the message does not contain, which is the single fastest way to earn a spam complaint from somebody who opened.

The three lines are read together

An inbox shows a sender, a subject and a preview, and they are read as one unit in about a second. Most senders write the subject carefully and leave the other two to chance.

• The sender name does most of the work. Recognition decides whether the subject gets read at all, which is why a constant name outperforms any individual line.
• The subject says what this one is. Short, specific, and accurate about the contents.
• The preview continues it rather than repeating it. By default it shows the first words of the message, which is usually a greeting, so it is wasted on hello.

Written as a unit, those three can carry a complete thought before anybody opens anything. Written separately, the subject fights for attention alone while the preview says the word hello.

A practical check: look at your own last send in your own inbox, on a phone, and read only those three lines. If they do not together say what is inside, that is the fix, and it is usually the preview rather than the subject.