There’s a well-known rule in journalism “You should spend as much time writing your headlines as you spend on writing the content” … For marketers, the same applies to the subject line of any email.

Your email subject line is the most importance sentence in any email. Why?

  • They are the first words your intended audience reads
  • They determine whether you grab your intended readers attention
  • They’re the call to action and determine whether the recipient opens an email or not

The average individual sends and receives 121 business emails every day, with this number predicted by experts to increase 3% year on year. If your subject line doesn’t grab them when they’re scrolling through their inbox, then you can’t sell them what’s on the inside.

Capturing your prospect’s attention with a subject line that intrigues them enough to open and read on is no easy task but there are 8 rules to follow to help increase your chances of success.

Keep it short

It’s always best to stick to 4 to 6-word subject lines of under 40 characters.

Many email service providers will cut off your subject line if it’s beyond a certain length. Viewing on a mobile device will also affect the number of characters in view.

Brevity can also lend an air of mystery and anticipation, encouraging readers to want more.  

Be positive

Try to use positive words in your subject line. Provoke interest by hinting at some benefit to the recipient if they go ahead and open. Any negative words or suggestions in an email subject are unlikely to encourage high open rates.

Avoid spammy characters or words

There’s a fine line between sounding enticing and using words that may trigger spam filters. Avoid phrases that may be construed as being pushy or misleading such as:

  • Act now
  • Buy
  • Bonus
  • Click here
  • Free
  • Money back
  • This won’t last

Avoid excessive punctuation

It’s best to use no more than 3 punctuation marks per subject line. Too many punctuation marks can make your email look like spam, especially if you use a lot of special characters.

Add an Emoji … with care

The debate about emojis continues, especially when it comes to their appropriateness in B2B communications but there is no doubt they are here to stay. Used sparingly they can help an email stand out in an inbox stacked full of text but keep them to a minimum to avoid diluting your brand and appearing spammy.

Write in sentence case

As a rule, capitalise the first word and any proper nouns in your email subject line. You may think capitalising the entire subject line will grab attention, but it can do the opposite and put your audience off.

Include a number

Like blog post headlines, using numbers in your subject lines increases email open rates. Numbers get your emails noticed and demonstrate a clear message.


If you’re still in doubt, try a tool like Omisend’s free Subject Line Tester. Just type in your carefully crafted words and it will instantly come back with a score and suggestions. 

Mike Harrison is Inbound Marketing Director at PR and Marketing Agency Essential Communications, a specialist PR and Marketing Agency for the tech sector and IT channel. As the ‘go to’ digital marketing lead within the agency, Mike is responsible for the delivery of all client and internal digital work.

Visit Mike’s LinkedIn profile here

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