How to Write Subject Lines That Get Your Marketing Emails Opened
The average person receives around 121 emails per day.
Let that sink in. 121 emails a day. With inboxes that crowded, your email has just seconds to stand out before it’s ignored, deleted, or marked as spam.
That’s where email subject lines come in. They’re the biggest driver of marketing email performance. In fact, 47% of recipients decide whether to open an email based purely on the subject line, while 69% will mark an email as spam for the very same reason.
So, how do you write an email subject line that actually cuts through the noise and grabs attention?
At Summary Content Marketing (SCM), email marketing is kind of our thing. Between us, we’ve been writing and refining email campaigns for over 20 years. Consider this your guide to crafting catchy, effective subject lines that get your emails opened.
What Is a Subject Line & Why Does It Matter?
Let’s take it back to basics.
An email subject line is “the short, bolded, and crucial line of text that acts as the title for your email, appearing in the recipient's inbox before they open it.”
It’s the first thing people see when they check their inbox. A subject line tells the recipient what your email is about and plays a key role in whether it’s opened, read, or ignored. In marketing, a compelling subject line is essential for standing out in crowded inboxes, and can be the difference between driving a successful campaign or watching it fall flat. Done well, it helps build a relationship with your audience, creating a strong, trustworthy first impression.
What Makes a Good Subject Line?
It’s common knowledge that no two subject lines should be written exactly the same, but the most effective marketing email subjects tend to follow a similar framework. Let’s break down the key elements that consistently drive opens.
Urgency
People hate missing out. Creating a sense of urgency encourages recipients to act quickly and pay attention. Phrases like “Limited Time Offer”, “Today Only”, or “Breaking” can instantly signal that your email is worth opening now.
Top Tip: Avoid overusing urgency. For one thing, it can trigger CAN Spam filters, and equally important, if every message is labelled “urgent”, it loses its thrill, and your email will lose its impact.
Personalization
Personalization plays a huge role in successful email marketing. Addressing your recipients directly makes your emails feel more relevant and human. Something as simple as using a first name, “Dave, we miss you”, can instantly grab attention and increase open rates.
Curiosity
A strong subject line sparks intrigue. When a subject line is short but hints at something interesting, it invites the recipient to open the email to find out more. Curiosity works best in email marketing when it teases value without revealing everything. Think “11 Hidden Secrets about [Topic]” or “[Product Name]: Your exclusive preview”.
Offers
Who doesn’t love a good deal? Highlighting an offer in your subject line can be incredibly effective, especially when it’s clear and compelling. Think “50% off”, “Free shipping”, or “Buy one, get one free.” It’s simple, direct, and hard to ignore.
Length
The most effective email subject lines are short and to the point, ideally 40–50 characters or 6–10 words. This ensures your message is fully visible on both desktop and mobile. Lead with your strongest, most impactful words to capture attention instantly.
Numbered Subject Lines
A number in your subject line sets people’s expectations and provides a structure for the content of your email. Try “5 Steps to Improve…” or “10 Things We are Loving”. The key to success with this formula is the number you choose. For steps in a process, stick to a low number to make it seem quick and easy. But if you’re sharing value, like ways to boost email subscribers, go for a higher number to show greater value.
Emojis
Emojis are fun and absolutely belong in your email subject lines. However, they should be used sparingly. One at the start, or the end of the subject line, works enough to grab attention; no more than three should be used. Additionally, emojis can be used to save space. Most subject lines get cut off by mobile devices after five words, so you could use relevant emojis in place of words.
Top Tip: Most mobile devices support emojis. However, you should verify that inbox providers recognize them, as this could trigger contact spam filters.
Get More Out of Your Email Subject Lines
Here are some additional helpful tips to ensure you get the most out of your marketing email subject lines for your brand or business.
Add Your Recipient’s Name
Using a recipient’s name is a powerful way to instantly grab attention. It creates a sense of personal connection from the very first glance, making the email feel more relevant and tailored to them.
Why not try?
Happy birthday, [Name]! Look inside for your surprise
[Name], check out these hand-picked deals for you
[Name], We miss you!
Tap Into Popular Culture
If it aligns with your brand personality, don’t be afraid to lean into popular culture. Referencing a trending meme, cultural moment, or major event can instantly catch your recipient’s eye. These shared references act like an “in-joke,” helping to build familiarity, spark interest, and strengthen the sense of connection between your brand and your audience.
Why not try?
“TGIF! If you’re happy and you know it…”
“How to leverage [Celebrity] for your sales”
"You left your cart… and your dignity"
Consider the Action You Want Them to Take
Every email has a purpose, and your subject line should reflect it. Whether your goal is to encourage a purchase, drive sign-ups, or prompt engagement, the subject line should clearly hint at the action you want the recipient to take. For example, if you want them to buy, referencing a deal, offer, or limited-time incentive can make that next step feel irresistible.
Why not try?
Sign up to reserve your spot
Claim your 20% discount - ends tonight
Come back! We saved something special for you
Email Subject Line Mistakes to Avoid
Even the best email marketing campaigns can fall flat or trigger spam filters if the subject line fails to hit the mark. While it can be tempting to chase opens at all costs, certain mistakes can damage trust, end up in the junk folder, and hurt long-term performance.
Clickbait that backfires.
Over-promising or using sensational language might get an open once, but if the content inside doesn’t deliver, your audience will quickly disengage. In email marketing, trust matters more than quick wins.
Misleading claims.
If your subject line suggests one thing and the email delivers another, recipients are far more likely to ignore future emails. Your subject line should always accurately reflect what’s inside the email.
Examples include:
An offer that isn’t actually free
Excessive steps that need to be taken in order to get something offered
Why Some Subject Lines Trigger Spam Filters
Even the best email won’t perform if it never makes it to the inbox. Spam filters scan subject lines for patterns commonly tied to junk mail. Certain choices can get you flagged fast.
Common triggers include:
Overly promotional language like FREE, Guaranteed, or Act Now
ALL CAPS or excessive punctuation!!!
Clickbait or misleading promises
Too many symbols or random emojis
Filters also factor in your sending history and engagement rates, so hype-heavy subject lines can quietly damage your deliverability over time.
Bottom line: write like a real person, not a late-night infomercial. Clear beats clever when it comes to getting past the filter.
Additionally, avoid subject lines that are too long or too generic. Long subject lines often get cut off in inbox previews, especially on mobile. Vague phrases like “Newsletter Update” or “Important Information” fail to give recipients a reason to open. You want to have a clear, specific email subject line to help set the right expectations from the start.
Need a Helping Hand?
Are you struggling to get your emails opened? At Summary Content Marketing, we are here to help you. From subject lines to full email campaigns, we’ll help you create emails your audience actually wants to open. Get in touch today, and let’s make your emails work harder.
