Subject lines have long been considered one of the most important parts of an email. They can help you stand out from the crowd and quickly connect with customers. But, with inboxes getting ever fuller, marketers are constantly looking for new ways to make their subject lines stand out. One emerging trend is the use of hashtags in email subject lines.

Hashtags are used on social media sites (like Twitter) to help identify messages on a specific topic, i.e. #emailmarketing. They can help to stimulate a discussion as users can easily find all the posts about the subject they are interested in. Nowadays, as social media and email marketing become more integrated, more and more marketers are starting to see the benefits of using hashtags in email subject lines.

A study by Retention Science has found that subject lines of between 6 to 10 words produce the highest open rates. Any more words than this, and you’ll being see diminishing returns on your campaign. Hashtags are, by their very nature, short and descriptive. The can help you save space in your subject lines while helping to spark conversation between your customers and your brand. With hashtags, you’re campaign can seamlessly move between email and social media. This example from Garnier illustrates this perfectly:

Garnier Subject


However, hastags in subject lines should be used with care. Matt Caldwell, VP of creative at Yes Lifecycle Marketing, estimates that 4 in every 10 people don’t know what hashtags are. Using them requires you to have thorough knowledge of your customer base. Do they use social media? Will hashtags in emails appeal to them? Provided you know your audience, hashtags can be a useful tool in email marketing.