10 Proven Email Subject Line Tips to Boost Open Rates

Here are ten proven tips from the team at SendLab.io to help your emails stand out in crowded inboxes.

1. Keep It Short and Focused

Most inboxes cut off subject lines longer than 50 characters, especially on mobile. Aim for 5–7 words or under 45 characters. Shorter subject lines are easier to scan and perform better on mobile devices — where over 70% of emails are opened.

2. Personalise Where It Matters

Including a first name (like “Hey Sarah, got a sec?”) can increase open rates, but overdoing it looks robotic. Personalise when it feels natural — referencing a past interaction, location, or interest often feels more authentic than using a name token.

3. Create Curiosity Without Clickbait

Curiosity drives opens, but false promises destroy trust. Tease what’s inside:

❌ Don’t say: “You won’t believe this secret!”
✅ Do say: “The email tweak that lifted open rates by 30%”

Make sure your content delivers on what the subject line promises.

4. Use Action-Oriented Language

Subject lines that inspire action feel more urgent and relevant. Start with verbs like Discover, Try, Learn, Build, Fix, Save, or Boost — they naturally encourage engagement.

5. Avoid Spam Trigger Words

Certain words (“Free!!!”, “Act Now”, “Guaranteed”) can trigger spam filters. Keep it conversational, not overly promotional. Run your emails through a spam checker (like SendLab.io’s Deliverability Tests) before sending.

6. A/B Test Every Campaign

No one gets subject lines perfect every time. Use A/B testing to compare two versions — for example:

• Version A: “Improve your deliverability fast”

• Version B: “How to land in more inboxes”

Track open rates and use the data to refine your tone and structure.

7. Use Numbers and Specifics

Numbers add clarity and credibility. Instead of “Boost your open rates”, try “Boost your open rates by 27%”.
Lists like “5 quick fixes for low open rates” also perform well because they set clear expectations.

8. Leverage FOMO (But Gently)

A sense of urgency works — when it’s honest. For example:

• “Last chance to join today’s deliverability webinar”

• “Only 3 spots left for our free audit”

Avoid false scarcity; it damages trust and long-term engagement.

9. Match Your Preview Text

Your subject line and preview text should work together, not repeat each other. Use the preview text to expand on the promise of the subject line and give readers a reason to click.

10. Stay Authentic to Your Brand Voice

Whether you’re professional, playful, or technical, consistency builds recognition and trust. Your audience should instantly know it’s you from your tone — even before they open the email.

Wrapping Up

The best subject lines are simple, honest, and intentional. They speak to the reader’s needs, not your agenda. Test regularly, watch your data, and always prioritise clarity over cleverness.

At SendLab.io, we help marketers and businesses improve email performance — from design and copywriting to deliverability and strategy.

👉 Learn how SendLab.io can help improve your deliverability.