The subject line is one of the most important parts of an email

The advertising legend David Ogilvy, founder of Ogilvy & Mather, once said: “Five times as many people read the headline as read the body copy.”

Like the headline on a blog post or a news article, your email subject line has to catch attention and persuade people to open the message. The subject line can make or break your email, so it is worth spending the extra time to craft one that is memorable and effective.

There are five common mistakes to keep out of a subject line, because they stop readers opening your email — or worse, fail the spam filter, land you in the spam category, and damage your reputation.

1. All caps, heavy bold, or too much punctuation, especially exclamation marks Sometimes the harder we try to be startling, the more we frighten readers off. They notice the intent and ignore the care that went into it. A better approach is to build the subject line around a concern that genuinely affects the reader — it reads as warm and considerate.

2. Using spam words Adding certain trigger words to a subject line can activate the recipient’s spam filter even when the message you sent is legitimate. Examples: “100% free”, “cash payment”, “cheap”, “lose weight”, “instant cash back”, and so on. These look like popular topics that everyone cares about, but they are already on record as spam keywords because they read as sales language. We are not in a hurry to sell in the subject line — we are pointing out why this email matters to the reader.

3. A subject that runs too long Avoid going on at length. Think about the environment your reader is in: very likely scanning the inbox on the move or between meetings. You have only a few seconds to catch their attention, so make sure the subject line is not long-winded or cluttered.

4. Writing something misleading Nobody likes being deceived, least of all when an email promises one thing and delivers another. You may get the initial open, but you alienate readers, and over time that hurts both your open rate and your spam-folder rate. Once subscribers lose trust in your email, they are far more likely to ignore future messages and mark you as spam.

5. Spelling or grammar errors in the subject Misspelled words and misplaced punctuation in a subject line look unprofessional and can damage your open rate. Email is an opportunity to establish your brand as a useful source of information. A subject line with spelling or grammar errors makes a poor first impression and undermines your ability to build trust with subscribers. To optimise your email revenue rate, always review grammar and spelling before hitting send. If the subject line is loaded with errors, nobody will spend time on the email.

The subject line is one of the most important parts of an email, so getting it right before you send matters. Avoid the mistakes above and you will go a long way toward improving your email engagement.