Why It Matters
47% of email recipients decide to open an email based on the subject line alone, according to OptinMonster. It's your first impression and often your only chance to earn an open. No matter how good your email content is, it's worthless if nobody opens it. Subject lines also directly affect your engagement metrics, which in turn influence your sender reputation and deliverability.
How It Works
Subject lines display differently across email clients. Gmail shows about 70 characters on desktop but only 40 on mobile. Outlook shows around 60. Since over 60% of emails are opened on mobile devices, your key message needs to land in the first 40 characters. Everything after that is bonus text that might get truncated.
Quick Tips
- Keep it under 50 characters for the best cross-device compatibility.
- Personalization works — subject lines with the recipient's first name see 22% higher open rates on average.
- Ask a question or create curiosity, but deliver on the promise inside the email. Clickbait subject lines spike complaints.
- A/B test subject lines on 10-15% of your list before sending the winner to the rest.
- Avoid spam trigger words like "free," "act now," "limited time" in isolation — they're fine in context but risky when overused.