An email subject header line, also known as an email subject line, is a brief summary or headline that appears in the inbox of an email recipient. The subject line serves as a preview or summary of the content of the email, giving the recipient an idea of what the email is about and whether it’s relevant to them.

A good subject line can entice the recipient to open the email, while a poor or unclear subject line may cause the recipient to ignore or delete the email without reading it. Therefore, crafting a clear and compelling subject line is an important part of email marketing and communication.

1. Keep it concise: A good subject line should be short and to the point, ideally no more than 50 characters.
   
2. Be specific: Your subject line should accurately reflect the content of your email, and be specific enough to give recipients a clear idea of what to expect.
   
3. Use action-oriented language: Use action verbs and language that conveys urgency or importance to encourage recipients to open your email.
   
4. Personalize it: Address your recipient by name or include other personal details to make the email feel more relevant and engaging.
   
5. Create a sense of curiosity: Use questions or intriguing statements to pique the recipient’s interest and encourage them to open your email to learn more.
   
6. Avoid spam trigger words: Avoid using words that are commonly associated with spam, such as “free,” “guaranteed,” or “limited time offer.”
   
7. Use emoji strategically: Emojis can help your subject line stand out, but use them sparingly and only if they are relevant to the content of your email.
   
8. Test different variations: Experiment with different subject lines to see which ones perform best, and use A/B testing to optimize your subject lines over time.
   
9. Make it mobile-friendly: Keep in mind that many people read emails on their mobile devices, so make sure your subject line is easy to read on a small screen.
   
10. Don’t mislead or deceive: Your subject line should accurately reflect the content of your email and not mislead or deceive your recipient in any way.