27 Sloppy Mistakes to Avoid in Cold Email Outreach Subject Lines

Andy Cabasso

December 10th

A cold emailing strategy focuses on sending emails to people you’ve never met or talked to before. And because this alone wasn’t difficult enough, keep in mind that the subject line is the first thing your recipients read. Do it right and it will boost your email open rates!

It’s easy to make mistakes in these situations and, unfortunately, it’s even harder to fix them. Especially when everyone seems to tell you completely different things about what you should do for a successful cold email outreach strategy.

To make things easier for you, I made a list of 27 things you should avoid at all costs. You can save these tips as a checklist template for later. Once you checked all the boxes and made sure you avoided all these common mistakes in your email campaigns, it means you’re ready to press that Send button! 

1. Not Including a Subject Line

Email subject lines are crucial because they give your recipients an idea about what your email body is about. 

forgot email subject line finding nemo meme

If you don’t include a subject line at all, your prospects will automatically delete your email or put it together with all the other spam emails. 

No subject line means no reason to open your email. In the long term, this is going to hurt your deliverability rate. And, worst-case scenario, your email service provider will flag your email address as spam and your domain gets blacklisted. 

2. Making It Too Long or Too Short

A compelling subject line will get your recipient to open your email because it provides some kind of value for them. 

You can’t possibly talk about something valuable by summarizing it in just 1-2 words. Similarly, if your subject line is too long, it means that you’re beating around the bush and people will lose their interest. So if your subject line has more than 11 words, it’s time to rephrase it with fewer words. 

Research shows that subject lines with 6-10 words have a 21% open rate compared with the ones that have 11-15 words (only 14% open rate). 

3. Not Optimizing for Phones

Considering that more than 50% of global website traffic comes from mobile accounts, not optimizing your subject lines for phones is a pretty bad move. 

optimizing email for subject line

Craft your subject line based on these factors: 

  • Desktop inbox shows around 60 characters
  • iPhone inbox (in portrait mode) shows 41 characters
  • Android inbox (in portrait mode) shows 30 characters. 

If your subject line is truncated in any way, your message might look too long and it will have a negative impact on your reply rates. 

4. Over-Promoting Yourself 

Sometimes, you might be inclined to prove yourself with a lot of testimonials, links, and credentials right from the beginning. 

But because your cold message should be short, it’s best to leave all these links for another time. Your subject line should focus only on communicating the benefits you can offer. 

And this rule is applicable for the email body as well. It is a common email etiquette to avoid including promotional words or too many links in your cold email message. After all, you’re sending a business email, not a newsletter! 

Don’t worry – you can send those extra links to boost your credibility once they reply or later, in the follow-up emails. But for now, your cold email subject line should be clean and straight to the point. 

5. Including Your Domain in the Subject Line

Your recipients already know who you are because of your email address.

Including your domain in the subject line would be redundant because you’re repeating information your prospects already know. 

Besides, take a lot at this subject line: 

Amazing collaboration opportunity for thisdomainwhatsoever.com!

You might as well send an email saying “Don’t open this message, it’s malware!” because these 2 subject lines have the same vibe. 

6. Not Adding Humor in the Subject Line

Sprinkle a few jokes here and there!It makes your message unique and shows off your brand’s personality.

Your subject line is already limited to a few characters so don’t waste the opportunity to craft an interesting, straight-to-the-point line that triggers your readers’ curiosity! Humor can be an efficient tool for an email marketing campaign! 

7. Using Gender-Specific Terms 

Avoid embarrassing situations like contacting the wrong person and using wrong gender-specific terms or pronouns. It shows that you didn’t do your research or that you don’t know who you’re talking to. 

 Plus, by using gender-neutral words in your subject line and your email body, you can prevent touching on sensitive topics like gender identity.

Just a few tips: 

  • Remove Mr. or Mrs. (that’s too formal anyway)
  • Replace businessman or businesswoman with a businessperson
  • Replace chairman or chairwoman with a chairperson

To make your subject line sounds a bit more personal and direct, you can use your prospect’s first name.

8. Not Personalizing The Subject Line

Another common mistake is that people do their research and find enough information about their prospects, but for some reason, they don’t use it to personalize subject lines.  

didnt personalize enough sad girl meme

If you’re being too bland in your subject line, your potential customers might find it boring and delete your message. 

On the other side, a fully customized subject line will grab their attention in a second! And that’s because people are more likely to respond to your message when you address them directly. 

9. Personalizing The Subject Line Too Much

But just a few seconds ago you said that it’s ok to personalize

You’re right, yet balance is everything. It’s ok to include personal details (like your prospect’s name or their company name) to customize your subject line. 

But don’t cross that line where you start sounding more like a stalker. You’ll scare them away and your email address might get reported too. And that’s because hearing a stranger mention personal details will creep out anyone.

Needless to say, but I’ll say it anyway – don’t talk about anything other than their professional life. Being creative shouldn’t land you in jail.

10. Using Outdated or Wrong Information

Don’t misspell your prospect’s name or company name, or use outdated personal business information in a subject line. 

Statistics show that data decays about 2% per month and that means that in a year, more than 20% of your data will become unusable. 

Broken personalization makes your brand look unprofessional and superficial. Before sending an email, do thorough research on your prospects and make sure that you have the correct name, company name, status in the company, and a valid email address. 

Don’t send your emails hoping for the best. When you’re not 100% sure that your cold email will reach the right person, be honest and ask for directions. 

11. Using Clickbait to Boost The Open Rates

Clickbait can be a very poor marketing strategy, especially if you’re using it in your cold email outreach strategy

You might think it’s a good way to improve your open rates or click-through rates, but it’s quite the opposite. 

If you’re using shocking words or fake claims just to get your prospects to open your cold email, they’ll leave the second they realize they’ve been lied to. This increases your bounce rate, lowers your customer engagement, and gets your email address blacklisted.

Besides, clickbait is easy to spot. Be sure that if you’re using clickbait even once in your subject line, all your future emails will land directly in the spam folder.

Don’t include cheap tricks like Re: or Fwd: in your subject line just to give them the impression that they’ve talked to you earlier. On the same note, don’t use a misleading subject line that has nothing to do with your email body. 

12. Using Filler Words

Linguists discovered that we tend to use filler words (like adjectives or adverbs) when we try to be more considerate to others and make our message less pushy or less urgent. But you can be polite even without all that fluff. 

Besides, using filler words eats a lot of character space in your subject line, makes it look vague, and doesn’t offer any valuable information. 

13. Making Absurd Claims 

No one believes those anyway! People tend to stay from too-good-to-be-true statements because in many cases they are just scams or lies. 

absurd claims million dollar austin powers

Don’t include subject line formulas that make you look like a spammer: 

  • We will rank you in 1 week
  • Our emails have a 99% open rate
  • We can increase your sales by $10 million per month
  • We’ve created the best marketing tool ever

This practice makes you lose credibility with your recipient and, depending on what action your readers might take, your email address is at risk of being blacklisted.  

14. Using Slogans

Slogans are a great idea for a newsletter, but you shouldn’t use them in your cold outreach strategy. 

Avoid including things like: 

  • This is your Black Friday opportunity 
  • Autumn project collaboration proposal
  • Summer has arrived and so have our discounts
  • The holiday season is approaching so here’s an idea!
  • I tried these black-hat SEO techniques for a month so you don’t have to 

Your subject line should be catchy, but don’t make it sound like a Vice copywriter wrote it. 

15. Using a Too Informal Approach

Just because you and your potential clients have a mutual acquaintance that doesn’t mean you’re friends with them already. Being too formal too soon can confuse your readers and make them feel uncomfortable. 

Your subject line should have a business or business casual approach.

16. Avoiding Prospect Segmentation 

Your prospects are different and have various needs, so a one-size-fits-all subject line is not always doable. If you use the same cold email template on everyone because you’ll be irrelevant to some of your readers.

divide and conquer marketing meme cat email outreach

And if you think about it for a moment, you’ll realize that even you have different reasons for reaching out to them. Maybe you want to collaborate on a guest post, or you want to congratulate them on a recent event. 

To avoid confusion, make sure that your subject line is personalized for everyone on your mailing list.

17. Making Grammatical Errors 

Before sending your message to your email list, double-check your subject line (and your body email) for grammar errors. Your subject line shouldn’t have: 

  • Incorrect verb tenses or forms
  • Misspelled words
  • Omitted commas
  • Missing prepositions
  • Subject-verb disagreements

Grammar mistakes decrease email engagement because it makes your message look like it was written in hurry. 

18. Using Bad Formatting 

The words are the ones that grab your recipient’s attention, not the way you’re formatting them. A minimalist, clean, and simple subject line is more natural and attracts more positive responses than a weird-looking one.

Avoid doing this, OR THIS, aNd DeFiNiTeLy tHiS. 

19. Using Special Characters or Too Many Emojis

Special characters don’t make your subject line look special because a lot of spammers tend to use them in their emails.

Don’t insert: 

  • Too many exclamation or question marks
  • Hearts
  • Arrows
  • More than 2 emojis 

The good news is that using an emoji in your subject line might increase the open rate by 29% and the click-through rate by 28%. And you get bonus points if you use your prospect’s favorite emoji! 

But keep in mind that even though using emojis gives your subject line a personality boost, don’t overuse them – words are by far more valuable. 

20. Using Spam Words 

Email service providers have built-in spam filters that get triggered anytime you use a spam word in your marketing email. You’ll end up sounding desperate and exaggerated so avoid using words like: 

no spam offer hello sir
  • Cancel at any time 
  • No gimmick 
  • No hidden cost 
  • Dear friend
  • Hello Sir
  • We hate spam 
  • Not junk 
  • This isn’t a scam

And if you think it’s a good idea to risk your subdomain to get flagged as spam just to make your subject line more interesting – you might want to reconsider. 

Once your email service providers blacklist your email address, it’ll be very hard to recover from that situation. You’ll have to request all your existing customers to white-list your domain, and you’ll have to hire a professional email marketer to analyze your bounce rate and come up with a newer and maybe not-so-successful cold email strategy. 

21. Using Custom Fonts

Personalizing your subject line with custom fonts is another common mistake. 

Keep in mind that even if we’re talking about a subject line with a few words, you still have to think about offering a good user experience. 

Custom fonts are not always supported and might get displayed with errors or at the wrong size. Besides, custom fonts may appear different on a mobile device than on a desktop. 

Consistency is key. Use the same fonts for all subject lines and make sure it’s clear and legible. Even if it’s a basic font.

If you think that a certain custom font represents your brand’s personality, you can use it to highlight that company trait. However, don’t use more than one email font because it makes your email hard to read. 

22. Being Too Vague

The role of the subject line is to get the recipients to open your email. If you’re being too vague, then the prospect has no reason whatsoever to prioritize your email and open in. 

Your subject should let your potential customers know what’s in for them or how your brand can make their life easier. 

If you’re too vague hoping that they’ll get curious and open your email, it will surely backfire. You need to get them curious and excited about your message. 

23. Using Common Templates You Find on The Internet

Let’s say you’ve found this super popular subject line template that everyone guarantees it’ll boost your open rates. 

Don’t use it just because it’s popular. You don’t know how many other brands used it as well and sent your prospects the same subject line just a few minutes ago. 

Create your own subject line to start a conversion – one that’s built around your brand’s personality and the ways you are as a business person. Yes, even if that means you’ll have a simple subject line – less is more. 

24. Forgetting to Mention The Urgency

Urgency helps your potential clients to make a decision faster. 

Sometimes, your recipients don’t know if your message is urgent or not, so they won’t prioritize it. Crafting a subject line that creates a sense of urgency or scarcity can boost your open and click-through rates. 

Anyway, don’t exaggerate with the sense of urgency because you’ll risk putting too much pressure on your prospects and they’ll feel overwhelmed. 

25. Forgetting to Mention The Mutual Friend

Another frequent mistake is to forget to include your mutual friend’s name. 

From your readers’ perspective, it might look like they’ve been tricked to open your email, and, as a result, they might get frustrated and block your email address. 

Keep in mind that if you reach someone by mentioning a mutual friend, let them know who you’re talking about and a full context about your conversation. Don’t let them guess who you’re referring to or, even worse, assume that you’re a scammer who happens to know the name of their friends. 

26. Using Different Subject Lines in Your Follow-Up Email

This rule applies only if you’re running an outreach campaign though. 

Instead of sending your prospects a new subject line for every follow-up, it’s better to keep your subject line the same in your follow-up emails as well. 

Otherwise, you’d have to reiterate everything that you’ve told them in the previous messages, and that would take too long and look unnatural. 

By keeping your subject line the same, your email is threaded, and they can respond faster to your first email. 

27. Not Researching Marketing Trends 

What worked 10 years ago might not work today. If you use old information or marketing strategies, it makes your subject line look outdated. As a result, your cold email might get zero response. 

Make a habit out of constantly researching marketing trends and applying what you learn when you write your subject lines. Besides, algorithms and strategies change frequently, so you have to know how to stay relevant. 


Wow, there are a lot of mistakes you should keep your eyes on! 

But it’s good to be aware of these common mistakes people tend to make because, in the end, all your hard work won’t even matter if you don’t apply these rules when you’re writing your subject lines. 

in the end it doesnt even matter linking park

At first, it might seem like a huge interminable list you should read every time you’re doing a cold outreach campaign. But don’t worry – things are way simpler and quicker in practice. You’ll see that many of these rules stick with you right after your first cold email campaign. 

A well-written subject line makes your prospect’s decisions easier and gets them excited or curious about your product. As long as you keep your subject line short, catchy, and fully personalized to your recipients’ needs, you’ll surely boost your click-through rates right from the first campaign! 

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