Examples of bad email subject lines:
- News
- Hey
- Hey! <- not just bad, exclamatorily awful
- Today
- <- See how little sense that one makes?
- Computer
Examples of good email subject lines:
- Grandma Injured in Fall
- Puppy Shipment Notice
- Utopian.net Invoice: PHP Programming example.com
- Utopian.net Invoice: Hosting Subscription <- notice the clever use of a series!
- Summary Notice to Cease and Desist Libelous Publication
You get the idea. It’s not like this hasn’t been covered at length. It’s in the RFC, from 1983:
The Subject line … should be suggestive enough of the contents of the article to enable a reader to make a decision whether to read the article based on the subject alone. - RFC 850, Standard for Interchange of USENET Messages