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What is an email subject line if not your email’s first impression when it lands in a prospect’s inbox? And emails are big business. Marketers sent over 838 billion emails in 2013 (that’s all the stars in the Milky Way times three).

That’s 838 billion subject lines. And with that many emails landing in prospects’ inboxes, they’re getting savvier than ever. Crafting the perfect email subject line can make or break whether your email is opened or not.

Unfortunately, with all the pressure of an introduction on an email subject line, they can become incredibly stressful. It is easy to start overthinking. Is it too long? Not intriguing enough? Too generic? Should I use emojis?

If you’ve ever wondered how to know what email subject lines to avoid, you can follow these general rules to give yourself the best chance at a high conversion rate.

  1. Subject lines with words that trigger SPAM filters.

The death knell of any email is when it get caught in a SPAM filter. If your email gets caught, the chances that your prospect will open and read your email drops to virtually zero. One great step is to look up lists of words and phrases that commonly trigger SPAM traps and ensure you haven’t included any. This will vary depending upon your industry, but a quick Google search will turn up the biggest culprits. In this list of email subject lines to avoid, this is the easiest one to implement and can make the biggest difference. Not only will it help ensure your emails make it to their destination, but it can help avoid triggering unconscious alarm bells that could make your prospect click away.

  1. Subject lines that ask for time.

Time is the only finite resource. We can’t make more time. So when someone bestows their time to you, it’s a precious gift. Keep this in mind when drafting email subject lines and try to avoid asking them for anything. This is especially true for cold emails. Your prospect doesn’t know you, might not know your company, and doesn’t (yet) care what you can do for them. Until they understand why you’re contacting them, any request for a meeting or call will feel like a chore. Email subject lines to avoid like this include “Do you have 15 minutes?” or “Can we have a quick chat?”

  1. Subject lines that have typos.

Typos look sloppy and unprofessional. They can also give off an air that says, “Hey, I’m new!” If you aren’t taking the time to run a spell check before pressing ‘Send’, your prospects might wonder what else you will cut corners on. Grammarly is a great extension that’s free and checks your spelling on emails and websites.

  1. Subject lines with your company name or branded terms.

This comes down to clarity. Chances are, your prospect hasn’t heard your company’s name before. If they aren’t familiar with your company or branded terms, this will just create confusion. You want the value of your email to be immediately apparent. You do that by putting the customer first. How? Use language your prospect will understand. Google and Apple have created billion dollar corporations using simple language that immediately conveys value. While it’s a tall ask, that’s what you want to do with your email subject line.

  1. Clickbait subject lines.

Just like with video or article titles, you shouldn’t put ‘clickbait’ in the email subject lines to avoid category. A common tactic among digital marketers is putting “Re:” at the beginning of the subject line. This works by tricking a prospect into thinking there is an existing conversation. Essentially, you want to avoid email subject lines that entice your prospect to click for the wrong reasons.


Phew. Caps lock is the digital equivalent of yelling. While it might make an email standout in an inbox, it’s not in a good way. Using exclamation points falls into the same category.

Getting it right.

Now that you know what email subject lines to avoid, we’ve rounded up a few quick tips for what you should do when drafting the perfect subject line. If you review the six types of email subject lines to avoid, you might see one theme in common. You want to avoid coming off as ‘salesy’ or ‘spammy’. These tips also follow a theme that will help you sound like a real person that can actually help.

  • Use spellcheck. Take a moment and download Grammarly if you don’t have it already.
  • Be short and sweet. Research has shown that subject lines under 50 characters have the highest open rates.
  • Show value. The only thing that matters to your prospect is how you will make their life easier. Make this as obvious as you can in your subject line.
  • Personalise it. Nothing turns off a prospect faster than the feeling that you sent out a generic mass email. Personalise the subject line to speak to one person at a time to increase conversion by 6%.
  • Shout out connections. Did someone suggest you contact your prospect? Using a mutual connection to warm a cold prospect is a great way to entice someone to click ‘Open’.
  • A/B test. The best way to know what works and what doesn’t is to test it. Send out two groups of test emails, each with a different subject line. Which has the highest open rate?

Email marketing is still a powerful way to win new customers, spread the word of your company, and meet sales quotas (especially when you have software on your side). Learning to craft the perfect email subject line that will get prospects eagerly clicking is worth the time investment. Fortunately, the few quick guidelines outlined here will make it much easier to avoid the common pitfalls of bad email subject lines.

Do you have a mental list of email subject lines to avoid? Let us know which ones you can’t stand in the comments.