The following is a revised and updated version of a previously published post, that takes into account new research published by our resident email marketing expert Parry Malm, as well as numerous expert sources, our own research and my own personal experience.

Sale now on!

Who cares? You’re always having a sale, why pay attention this time?

Also according to MailChimp, free tends to trigger spam filters, as well as help, % off and reminder.

However the old adage that ‘sales messages trigger spam filters’ isn’t necessarily true anymore. 

Just describe the details of your sale in the most straightforward and concise manner possible, without relying on manipulation. 

If you’re a company that hasn’t been mixing up its marketing messages and instead bombarding your recipient’s in-box with repetitive offers saying deals or sale ending soon, you’re just going to get ignored.


As Parry Malm stated in his article on split-testing subject lines perfect reduces open rates by -28% and the most mediocre adjective good reduces open rates by a not-so-good -20%. Also watch out for wonderful which is… uh… less than wonderful.

Days of the week

According to Alchemy Worx, days of the week cause a drop in open rates. Especially Monday and Friday. This is probably due to the sheer volume of emails sent to promote Cyber Monday and Black Friday.


Mailchimp has found that donate is a big loser for open rates. Help and assistance are also to be avoided. However in slightly more heart-warming news, fundraising is fine. 


Using numbers may help quantify your message, but constant sales and promotion emails can lead to fatigue. Mix it up as much as you can.

Tired internet slang

If it hasn’t dated already, chances are for some people it already has: bae, fleek, dat, basic, derp, cray-cray, ftw, yort, AF, flex…

I have so may negative feels towards the above. I also may have made one of them up.

Oh and hashtags serve absolutely no purpose in email subject lines. In fact they may even hinder a recipient’s ability to search for your email.

Deceptive familiarity

FWD: and RE: the artificial adding of ‘Fwd:’ or ‘Re:’ to trick you into thinking this is part of an ongoing conversation you’re engaged with already only creates distrust.



Content marketing

According to Adestra, content marketing headlines that use report (-23.7% opens, -54.8% CTR) and webinar (-16.6%, -70.7%.) fail to live up to expectations. As do the words book and learn, you uneducated lot.

Video, news and bulletin do work well though. As does the word ‘content’ itself.

Erroneous personalisation

Personalisation means nothing if your data isn’t correct and you don’t have 100% confidence in it.

“Paul check out these amazing offers!” when my name is Christopher, or even worse “[test] check out these amazing offers!”

In fact using a person’s name doesn’t really impact the open rate anyway, and can come across as needy or begging.

Punctuation shame corner

All of these…

  • Exclamation marks – the more there are, the less likely I am to open it.
  • Stars, squiggles, indistinct shapes – basically anything that isn’t actual text.
  • Hearts – bleuggh! 

[Putting anything in square brackets] or immediately makes you think there’s been a coding error.

Although just to add balance, I did learn that travel site Travelocity achieved a 10.7% lift in unique opens by using a little airplane in its subject line. Which proves that relevancy to content and uniqueness is imperative to proper symbol use.

However, just remember that symbols appear in some email clients but not others, so it may just be a waste of time anyway.

Which leads me to the subject you’ve all been waiting for…


David Moth covered emojis in emails earlier in the year, but I shall condense the hard-hitting research here.

Pointy finger, sunshine and the number 10 are all bad according to Alchemy Worx. Snowman ftw though! Sorry I broke my own rule there.

The question of why the black sun increases open rates by 20.95%, while the white sun causes a drop of 8.03% has yet to be answered.

Other personal grudges

Awesome: Just stop using it. Everywhere. At all times.

TBT: so bored of ‘throwback Thursday’.

I could probably end this article with a torrent of of all the different swear words I know, but being as I have no proof that these would negatively impact open rates, it wouldn’t be scientifically correct to do so.

Further reading

For more on the proper use of email subject lines, check out these vital blog posts: Email marketing subject lines best practice, six case studies and an infographic on how to write effective email subject lines and 152 killer keywords for email and 137 crappy ones.