1. Subject lines that resemble spam

The first thing you do when you see an email in your inbox that looks like a sleazy marketing offer is to delete it or mark it as spam. That's why one of the worst things you can do is write a subject line that looks like you're selling male enhancement pills.

Some common indicators of mass marketing emails include capitalizing the first letter of every word (or even all capital letters), using trigger words like free, save, click, and offer, along with ending subject lines with one or more exclamation points.

Instead of coming across as an unsolicited mass marketer, sales emails need to seem like one-on-one communications if you ever hope to get a positive response. Instead, strive to have your emails resemble personalized notes that feel like one-on-one conversations, even if they are mass.

2. Fake familiarity with “Re:”

One effective tactic for encouraging a recipient to open a sales email is to camouflage the subject line as a reply to an ongoing conversation, or otherwise make it look like something that belongs in the recipient's inbox (e.g. “the info your assistant requested“).

While you might believe this is a great way to get your email opened, using this technique can actually increase your odds of going to spam. Mail servers are trained to recognize this cheap trick. Likewise, the recipient will immediately realize that you've duped them, leaving them annoyed and insulted. Not only have you alienated a potential customer, you might even create a new critic of your company's brand.

3. Brevity is best

Whether your email is received on a computer or mobile phone, chances are that the recipient sees only a preview of your subject line–the first six or seven words on many mobile devices or tablets. So if you've written a long, enticing subject line, you've probably wasted your time, since most of it will never show up in their inbox preview.

When it comes to subject lines, brevity is often more persuasive anyway. For example, which one do you prefer: “5% increase in annual recurring revenue = 3-4x marketing return“, or “boost your ARR now“?

Think of the longer subject line as similar to an incomplete thought: if the reader doesn't see all of it, they can't understand all of it, and its power to persuade is greatly diminished.

4. Focusing on yourself instead of the customer

Subject lines like “[Product] Launches in 4 Days!” are ineffective because they assume the reader is interested in your company and its offers. That might work fine in an email from a drip marketing campaign, where someone has already expressed an interest in your brand. But with cold emails, this kind of narcissism is a kiss of death.

To entice someone to read your email, you must first provide them with a distinct value proposition. Why should the reader care that your product is getting ready to launch? What's in it for them? Write the subject line in terms of the recipient's own problems and needs, and you'll instantly grab their attention. Suddenly, “[Sales Product] Launches in 4 Days!” becomes tips to boost your sales efficiency by 22%“.

5. Disappointing clickbait with no follow-through

A racy subject line with big promises might get an email opened, but the opportunity will be ruined if the email's body doesn't deliver on the promise made. For example, if your subject line promises to “3x {!Company} leads in 3 to 5 days,” but then the email goes on to describe a weeks-long integration process, your entire message has failed.

Clickbait subject lines that fall short undermine your efforts, destroy your credibility, and leave readers feeling swindled. Too-good-to-be-true subjects only work if you can back them up with a concrete offer and social proof that matches your claims.

What other subject line fails have you seen in your inbox? I'd love to hear about them, and I might even include them in a future piece.

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