Apple really wants developers to incorporate the iPhone's newest feature into apps
Introduced on the iPhone 6S in September, 3D Touch measures the pressure on the screen and can perform different actions based on that result.
Users can can "peek" or "pop" an app, showing a little amount of information before the full app opens.
Apple has been working on raising awareness among users of 3D Touch, which is invisible to the naked eye, by advertising it heavily.
The email was sent to an unknown amount of developers.
"iPhone 6S and iPhone 6S Plus are now in the hands of millions of customers around the world," it reportedly reads. "The response has been incredible."
The company goes on to describe 3D Touch as an "exciting technology that senses how deeply users press so they can complete essential tasks more quickly."
Many developers are including 3D Touch features, including Adobe, Amazon, Facebook, Google, and Microsoft. However, some have not and it appears that Apple is evidently trying to reach them.
Here is a screenshot of the email:
