WWDC 2021: MailKit set to offer new Mail extension possibilities

By Stephen Hackett

For many years, power users have been able to use plug-ins to extend the capabilities of macOS’ built-in Mail application. And for years, those users have been accustomed to those plug-ins breaking as Apple has updated Mail and the operating system.

This year at WWDC, Apple introduced MailKit, a new Mac-only framework for building modern Mail.app extensions. This framework is based on the same underlying technology that powers Safari app extensions and share sheet extensions.

Mail Extensions

There are four types of Mail extensions:

  • Compose extensions will allow new workflows when composing mail messages.
  • Action extensions help people manage their inbox by providing custom rules on incoming messages.
  • Content blocking extensions provide WebKit content blockers for Mail messages.
  • Message security extensions can provide further security by signing, encrypting, and decrypting messages when people send and receive mail.

These extensions can be bundled into existing Mac applications, or be offered on their own, but must pass through the Mac App Store.

Time will tell what types of Mail extensions are possible in this new framework, but if Apple’s WWDC session about them is any indication, this should be an exciting change to an app that hasn’t seen much excitement or change in quite a long time.

Apple is clear that extensions are the future; existing Mail plug-ins will stop being supported in the future. While this means that some favorites may not be long for this world, I’m excited that Apple is now offering a sustainable, official way for developers to make Mail.app on the Mac more useful and flexible.

[Stephen Hackett is the author of 512 Pixels and co-founder of Relay FM.]

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