macOS Monterey to Support All-New Mail App Extensions, Plug-Ins Will Stop Functioning in Future Release

As part of WWDC this week, Apple introduced a new MailKit framework for macOS Monterey that enables developers to create Mail app extensions that block content, perform message and composing actions, and help with security.
There will be four main categories of Mail app extensions, according to Apple:Compose: Extensions that provide new workflows when composing emails
Actions: Extensions that apply custom rules to incoming emails, such as an email being color coded, moved to a separate inbox, ma