Subject Lines are the window to your content. It’s about balance. You want to create a curiosity gap, while at the same time avoid being click-bait. Keep in mind that lots of people can detect click-bait subject lines that are way too good to be true-and your open rate will suffer.
You never want to mislead your readers, but you also don’t want to give away all the value of your content in the subject line. Include enough information to strike interest, and once they click on, they’ll get the answer to the questions. Keep an eye on your open rates and click-through rates-these are your proof of performance for your subject lines.
If you don’t know much about creating great subject lines, we’d recommend doing split testing or A/B testing. A/B testing allows you to send two variations of the same campaign, by changing one aspect of one of your emails. For example, you could test two different subject lines. Doing this allows you to send version A to one sample group, and version B to another sample group, and track which email performs best. A/B testing can help you to determine what aspect of your campaign is causing low open rates or low click-through rates.
-Vendasta June 2019