How to write compelling cold email subject lines for superb open rates

The journey of a prospect through a sales funnel often starts with a cold email. In fact, the first few words are the subject line. If it’s not well written, then the open rates will be much lower, bringing in a lot fewer leads and consequently, sales. So, in this post, I will explain what makes good cold email subject lines to get high open rates. And a few important rules to keep in mind.

Before I start breaking down each topic, here is the list of them for reference:

Basic rules for a good subject line

  • avoid spam or clickbait
  • keep it around 60 characters
  • use relevant symbols and numbers
  • personalise with placeholders

Examples of subject lines and their breakdown

There are more rules than the ones I am about to show you. But, they are relevant and can boost your open rates as soon as you implement them.

1. Avoid spammy or clickbait subject lines

“69% of email recipients report email as spam based solely on the subject line.” – Invespcro

Using tricks to make targets open your email may work. But if the email does not deliver on the expectations, then it will annoy and disappoint the prospect. They will remember you and your company in a negative light. So, adopting clickbait fails to get the prospect to reply. And it causes damage to your image and that of your brand’s.

2. Keep the number of characters around 60

The prospect’s screen will show a maximum number of characters of your subject line. That number will determine the length of your subject. Desktops and tablets (landscape orientation) display between 40-70 characters of the subject line. Smartphone screens show 30-60. So, I recommend keeping the number of characters around 60.

3. Use relevant symbols and numbers

Numbers and symbols can be used in subject lines with success. Follow the next rules to do it right:

Symbols like // and – and () can be used to separate and clarify the subject. Others like * ~ ^ % $ # should not be used because they are generally associated with spam emails.

A question can be a useful tool in a subject line because it provokes the curiosity of the recipient. However, by using more than one you eliminate its effect and it can even hurt your conversions.

Numbers should be relevant to the message. And any number below 10 should be spelt in the ordinal form (e.g.: one; not 1).

4. Personalise with placeholders

“Personalized subject lines are 22.2% more likely to be opened.” – Invespcro

Personalization is key to attain better conversion in your campaigns. So, for example, include the name of the prospect in the subject line.

The next level of personalization is using dynamic placeholders. They enable 100% customization of your subject lines to get even better conversions.

Examples of subject lines and their breakdown

Example 1 – the company team up
‘{{companyId.shortName}} + hubsell – how about we team up’

The subject line is good because it is personalised with their company name. It also creates a team mentality and goes straight to the point (teaming up).

Example 2 – the value proposal
‘Increase ROI through outbound optimisation with hubsell’

The subject line provides a clear value proposition and demonstrates industry knowledge. It also incites the prospect to obtain the value by opening the email.

Example 3 – the company team up
‘(If prospect is in business development) {{companyId.shortName}} + hubsell – business trends and developments

(If prospect is in sales) {{companyId.shortName}} + hubsell – business leads and sales opportunities’

The subject line personalises according to the target’s department. It shows that the message is directed to them through the company name. And it plans to offer value and not just sell.


Writing your subject lines should be taken seriously by any demand generators. Hopefully, this blog post has given you the main guidelines to follow and examples to inspire you. Here are the main takeaways from this blog post:

Basic rules for a good subject line

  • no spam or clickbait
  • keep it around 60 characters
  • avoid symbols and irrelevant numbers
  • personalise with placeholders


The latest B2B insights direct to your inbox.

Get weekly updates on the state of B2B from hubsell.

A quick guide to account-based sales

Although the account-based sales model has been here for a long time now, its popularity has consistently increased over the last few years. But, what exactly is it? Is it