Subject line best practices have evolved as both spam filtering technology and subscriber tolerance for manipulative tactics have changed, making genuine specificity and relevance the more reliable current approach compared to older curiosity-gap or urgency-heavy conventions.
Curiosity-gap subject lines ('You won't believe what happened next') have been used so extensively that subscribers, and increasingly spam filters, have grown resistant to them — genuine specificity now consistently outperforms that once-standard tactic.
Excessive urgency language, ALL CAPS formatting and manipulative curiosity gaps increasingly trigger spam filtering and subscriber fatigue, making them counterproductive relative to their intended effect.
General best practices provide a starting point, but per our A/B testing guide, testing subject line approaches against your own specific audience remains the most reliable way to confirm what genuinely works for your list.
Yes, shorter subject lines display more completely on mobile devices, where a large share of email is now opened — keeping subject lines concise is generally advisable.
This depends on your brand voice and audience — some contexts benefit from tasteful emoji use, while others may find it feels inconsistent with a more formal brand tone.
Yes, per our AI features comparison, AI-assisted subject line generation can provide useful starting variations for testing.
If you want help improving your email subject line performance, talk to our team.
Prioritise genuine specificity and relevance over curiosity-gap tactics or excessive urgency language — modern spam filtering and subscriber fatigue with manipulative tactics mean specific, honest subject lines now consistently outperform the clickbait-style approaches once considered standard practice.
Written by Fibvo — Bengaluru and Erode, India — working with clients in other time zones. Questions, or think we have it wrong? Tell us.
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