Email subject lines should be short, descriptive, and sentence-cased.
They should explain what’s inside, not sell it. That said, some form of benefit statement often translates to good open and click-through rates.
Questions are fine, and often perform very well.
The two most common subject lines we write are for:
1. New feature announcements
Ex: New feature: <NameOfFeature>
2. The blog newsletter
Ex: 9 UI design tips + free ebook
Obviously, subject lines are perfect subjects for A/B tests, so feel free to experiment with your alternates.
Some of our most-opened subject lines
Webflow CMS as landing page engine + How Webflow powers startup Payable 23.2%
The Future of Webflow in 2015 23.2%
Webflow CMS is here 22.6%
New feature: flexbox 20%
9 UI design tips + 3 design process tools 19.5%