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🆘Subject line A/B testing + how to improve them

Subject line A/B testing

This is Inbox Hacking, a free newsletter with unique marketing insights, tools, & tactics sent every Wednesday. Join marketers from Ad Age, Duke University, & Zoho, and sign up for your Free subscription

Inbox Hackers, we’re 2.5 days away from the weekend. Well, I’m .5 days away, but don’t be all jealous. Being lazy isn’t all it’s cracked up to be.

Onward. Today’s feature gives you 5 ways to test your subject lines, then improve them so you get more opens, and increased clicks / conversions. No time to waste. Let’s rip into it then we’ll get to our Knowledge Base, some anti-Self Help, and Today’s Hack has more inbox insights.

3 Key Reminders for Subject Line Testing

  1. Your email reading habits are not your audience’s reading habits
  1. Hot trends for stand-out subject lines cool off as the bandwagon grows
  1. Most marketers are afraid to test anything truly creative (get canceled, fired, or worse – promoted)

5 Subject Line A/B Testing Options

Drip listed 12 ideas for subject line A/B testing here.

Awesome. But seemed like a lot of work.

The simplest A/B testing options are:

A)Go all lower case or B)Start line with upper case

A)Start with emoji or B)End with one

A)Use numbers or B)No numbers

A)Parenthesis in subject line or B)Parenthesis in preview text

A)Create curiosity or B)Aim for urgency

Oh, if you ever consider A/B testing subject lines with exclamation marks, it would be best if you just cancel your internet.

Thoughts on Those Subject Line A/B Testing Options

I suggest all lowercase if you want to stand out a little. Not guaranteed to get the open rates you’re lusting after. But 99% of subject lines in my maxed-out inbox do capitalize the first word in the subject line.

Emojis should be used 90% of the time IMHO, regardless of starting or finishing with them.

Numbers produce opens. They make the content inside sound easy to digest.

Parenthesis are simply not used often, so they differentiate your message from the unparenthesis’d pile.

Work on ways to generate curiosity because urgency (big fan) isn’t always possible and can also be run into the ground!

3 ways to make even readers with ice-water in their veins curious:

  • Use gossipy language (irresistible to even emotionless sociopaths like myself)

  • Scrub bland corporate-speak from your brain (notes you take in meetings should be trashed ASAP)

  • Be intentional and write down things you notice that make you curious to read more about a topic (start in your inbox, then go to headlines on news sites, then to the first sentence of YouTube comments, etc.)

*Interesting facts are not enough… The topic must be perceived as valuable for curiosity to be stimulated. ~Semanticscholar.org

Below are a few headlines that riled up my curiosity (from the WSJ, not exactly click-bait central, so you won’t feel dirty):

  • The M.B.A.s Who Can’t Find Jobs
  • She Made the ‘Safest Space on the Internet.’ Now She’s Trying Something New.
  • ‘Peacock Game’: The NFL’s Digital Buttfumble

See what they did there? I wanna know why the game was a Buttfumble. I wanna know more about the internet’s safe space since I never fathomed a place like that existed. And I understand people with degrees being unemployed, but why are THESE specific ones jobless? 

A/B testing subject lines gives you helpful insights, yet…

It’s hard to overstate the lethal effect of curiosity. Kills a bunch of cats, even with all those lives. 

Point is this. Use those curiosity tips and tactics I dropped on you for improved subject lines. And one more tip— practice on subject lines you wrote in the past. What could you have removed from the line that would’ve made the reader more likely to peek inside to get that missing piece of info?


You Simply Lack 🫵Touchpoints

Look, the vast majority of your website visitors aren’t ready to buy on their first visit.

No problem, except they’ll likely buy from another website instead of returning to yours.

Why? Distractions, better deal, 101 reasons…

One reason you already know for sure? People won’t buy without multiple touchpoints.

Would you like those multiple touchpoints? Delivered on a silver platter?

You got it… through an AI-powered lead generation tool called Smart Recognition. 

This platform captures verified email addresses of up to 40% of your anonymous website visitors— interested prospects who would otherwise bounce, never to return. These leads are automatically inserted into your ESP or Network Audiences!

Schedule a free Smart Recognition demo now to see how you too can grow your email list fast… and increase sales like FinMC did.

“Within 72 hours, adding Smart Recognition to our sales process resulted in a 5x return on our initial investment in the offering.” -Morgan B., FinMC

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Knowledge Base

Knowledge is power, so is the refusal to stay down

❌Why no-reply emails are no-nos

🤓Updated tool for email nerds (others proceed w/ caution)

♠️Know when to fold ’em w/ content creation

🤗5 loyalty / referral tools on autopilot

🥴AI prompt engineering gurus – a dirty myth


self help

Self Help

Some folks in your life were valuable resources to you.

They helped you, knowing you couldn’t help them back.

A grandfather, aunt, neighbor, whoever.

Time constraints will prevent you from repaying that help to all those people. 

But one day you’ll find time to help someone else, in their name.

* Inbox Hackers Shout-out:

Catherine at Farmhouse Inn

Courtney at Shillington Box Company


Facts and Stats

  • Up conversion rate of abandonment messages to 6.33% by sending within an hour of a user’s online shopping session (Convince & Convert)
  • News sites’ traffic from Facebook fell 48% / traffic from X/Twitter fell by 27% in 2023 (Chartbeat)
  • 74% of consumers suspect online tracking still occurs even when they opt out (Email Insider)

Bonus: What deep work looks like (visual)


Crybabies, Meth-Head Fish, & Email Fails

Spam filters are hurting legitimate emailers.

Apple’s MPP is trying to put email marketers in the poor house.

And readers have the attention span of a goldfish on meth.

I guess we should all give up, go home, and cry about it?

Nope. No crybabies allowed.

Instead, why not do the simplest thing possible to improve your email deliverability…

Get subscribers to open more of your emails. How?

Inbox Mailers’ triggered emails. These emails skip the line at the inbox to ensure your emails get top billing so they get opened, then get clicked on (up to 70% open rates + higher click volume).

Demo Inbox Mailers and see how successful your email campaigns become when you can target subscribers while they’re actively in their inbox!

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Get Hacking

What stood out in my inbox this morning…

  • Only 10 outta 50 emails had emojis in the subject line
  • Just 2 of 50 used quotation marks around a phrase
  • 1 of the 50 used parentheses in the preview text

Little tweaks won’t guarantee opens but at least attempt to not look like the crowd. Review your inbox today to see what makes an email blend in with other easy-to-ignore emails.

🔎 “Did you find what you were looking for?” is a subject line that must work well for Harvard Business Review, else they wouldn’t keep sending it. No word on whether that line was plagiarized also.😎


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