One of the great things about running a sector agnostic outbound platform is that we have aggregated cross-industry intelligence. Our agents have sent millions of emails on behalf of our customers, and so we’ve come to learn a thing or two about subject lines; what works, what doesn’t, and how to play the game to win. So let's strip this back to first principles. 

Your cold email subject lines have one job, and it’s to get opened. Not close the deal. Not explain your product. Not win Cannes Lions. 

It’s remarkable how badly people get this wrong. You need to start by thinking about the concept of patterns, and what patterns mean to the spam filter bots of Microsoft, Google and the other mailbox providers. 

Real humans, when communicating with one another over email, display very few patterns of regularity. A ‘normal’ human will send emails for wildly different reasons, and therefore the subject lines and content will both differ from email to email. This is a foundational tenet of why AI generated emails perform better than templates at landing in the inbox; each message is different, therefore making it much harder for anti-spam bots to pattern match. 

So if you are using the same subject line again and again  in your outbound campaigns, you’re essentially flagging yourself. One way to get round this is to use a dynamic variable in the subject line eg. the {{company_name}}, such that every email subject line just contains at least a word(s) that is different every time. 

But I want to stretch beyond that and look at some other best practices that will help to avoid common pitfalls. Because let’s face it, even the best email in the world can fall foul of a crappy subject line. And if that subject line is the reason the email isn’t opened at all, what’s the point in even sending it? 

So here are 3 golden rules: 

Rule 1: Short wins 

• 2-5 words is the sweet spot a lot of the time 

• Mobile preview = cruel 

Rule 2: Specific beats clever

• Concrete > cute. “Quick question” is the beige paint of subject lines.

Rule 3: No weird energy

• Avoid spammy punctuation, false urgency, and “RE:” cosplay.

I dread to think how many messages currently sit in the graveyard of unopened emails. But given that it’s estimated 160bn+ cold emails are sent every single day, we can assume the number is pretty big. Here’s a snapshot of my spam folder today. Just look at the horrible subject lines:

These are the common mistakes people make with subject lines: 

1. Over-personalisation that looks weird and is clearly scraped 

2. Making them too long 

3. Fake forwards and ‘RE’

4. Spam words and punctuation 

Some old favourites that people think work include the dreaded:

• “Re: following up”

• “Quick question”

• “Thoughts?”

• “Meeting?”

• “Urgent”

The last one in particular raises another interesting point: spam words are real. And you need to make sure that they are in neither the body nor the subject line of your emails. Spam words are triggers, and are essentially a blacklist of high-alert words that filters find especially offensive. 

Anything that suggests excessive urgency, is related to financials, signals overpromise, or can be deemed as shady, will have a much higher likelihood of landing you in spam. 

If in doubt about what a spam word, run your email or your subject line through MailMeteor’s spam word checker here 

The key things are to keep it simple, avoid trigger words, and add dynamic variables where you can. Some that we’ve been using internally include: 

• “Perlon AI & {{company_name}} partnership” 

• “About {{company_name}}’s outbound”

• “{{first_name}} I did my homework”

• “Idea for {{company_name}}”

• “{{company_name}}’s Q1 strategy”

These, followed by a hyper-personalised, well researched and deeply relevant email bodies are what enable us to drive around 70% of our new business from cold outbound. 

If in doubt about your structure, feel free to book a call with one of our team and we’d be happy to sense-check any campaigns you happen to be running and help to optimise them where we can. 

May your open rates be high and your ‘Sent from my iPhone’ be low.