How to write a killer email marketing subject line

When it comes to writing the subject line for an email campaign all email marketers struggle from time to time.  It’s a struggle because you know that no matter how relevant, compelling and irresistible the content of your email may be, if it doesn’t get opened, you’re not going to get results.

Below we will give you some tips and solid advice based on many years of email marketing experience, to help take the struggle out of your subject line composing, and help you maximize your open and response rates.

Anyone involved with email marketing will find this study of interest. Whether working in a B2C, B2B or Non-Profit organization, marketers, designers, developers and technicians will find both inspiration and hands-on guidance in the results and recommendations provided.


  1. Rule number 1 is… there are no rules.  The way a group of recipients reacts to a given subject line will depend on who those individuals are, what their motivations are, how busy they are, how frequently you email them, etc.  Any number of variables may be in play, which leads us to rule number 2…
  2. TEST, TEST, TEST. There is no better way to learn and hone the most successful approach to subject lines for your target audience and your campaigns than by split testing them.
  3. Get the key elements of your subject line into the first 50 characters. There has been a lot of analysis and reporting into subject line length and what works best.  There certainly is no hard and fast rule that your subject lines should be short or should be long. But what they should do is deliver the key message or proposition within the first 50 characters.  That doesn’t mean they should only be 50 characters long – split test different subject line lengths.
  4. Avoid the ‘mysterious and oblique’.  Generally speaking, mysterious or vague subject lines that are designed to entice recipients to open out of curiosity, will not deliver you the metrics you want to see, i.e. high click through’s and conversions.  There are exceptions to this rule, but beware.  Focus on the objectives of your campaign before you choose this approach.
  5. Make the content of your subject line specific and single-minded.  Focus on the key message, offer or proposition in your email and spell it out clearly and succinctly in your subject line.  Specific, relevant subject lines are more likely to generate not only opens, but click through’s and conversions too.
  6. Tell – don’t sell. This doesn’t mean you shouldn’t put an offer in your subject line if it’s your key message.  It does mean you should keep the subject line factual and avoid those ‘Power Adjectives’.  If the offer is ‘20% off’ then state it, but avoid the ‘amazing 20% off’ in your subject line.
  7. Write your subject line AFTER you’ve written your message.  Many marketers do this the wrong way around. This is not a chicken and egg story – your content should come first.
  8. Test your email through a spam checker. This will highlight any issues within both your subject line and your content that may channel your email into junk boxes.  To ensure your subject line is spam filter friendly, make sure you avoid the use of capital letters and exclamation marks.  You can use the word ‘free’ but never use ‘FREE!’
  9. As with all your copywriting, you should know who you are writing your subject line for – who your target market is, who they are as people, what they do, what motivates them, how busy they are.  Put yourself in their shoes as a recipient of your email when you write your all-important subject line.
  10. Lastly, find inspiration in your own inbox.  It’s always worth signing up to your competitors’ emailing lists and those of other organizations relevant to what you do. Use a separate email account and check it regularly for subject lines that stand out and make you want to open the emails.  Save them in a word file and you’ll have ready-made inspiration when staring at that dreaded blank subject line field.

Testing your email subject lines

Subject line split testing should be an integral part of your campaign process.  Split testing simply means you take 2 different subject lines and send them to 2 samples of your target audience and measure which is the most successful – then use that subject line when you send to the remaining bulk of your list.

How do you measure success?

This depends on what you are aiming to achieve with your email campaign.  If you are spreading awareness or a branding message or running a teaser and you have no direct call to action, then your open rate stats could be your measure of success, i.e. what percentage of those who received the email, opened it.

If (as is more likely) you are driving traffic to your website or landing pages using links from your email, then you might choose to measure the ‘click to open’ rate of your split test, i.e. what percentage of those who opened the email, went on to click through.

If your email campaign has a final goal, i.e. to drive recipients to buy a product online, or to register for something on your website, or fill out a contact form, then you might want to look deeper at the conversion rate of the split tests.   Any of these measurements have their value – your choice depends how much detail you want to measure on and how much time you realistically have to invest in testing.

Your subject line testing shouldn’t be a one off.  What works in one month may not work in 3 months time.  That’s the nature of the game, so you need to test for each campaign on an ongoing basis.