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.

mail app extensions macos monterey
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, marked as read, or flagged
  • Content Blocking: Extensions that serve as WebKit content blockers for emails based on specific criteria in an email's HTML code
  • Message Security: Extensions that sign, encrypt, and decrypt emails when sending and receiving mail, with signed and encrypted icons below emails

Xcode 13, available in beta, includes a template for developers looking to create Mail app extensions on the Mac. The extensions can be built into existing Mac apps and can also be distributed through the Mac App Store, according to a WWDC session about MailKit, which is available on macOS only and not iOS or iPadOS.

In the WWDC session, Apple indicated that older Mail app plug-ins will stop functioning in an unspecified future macOS release.

macOS Monterey is available now in beta for developers, with a public beta to follow in July.

Related Forum: macOS Monterey

Popular Stories

iOS 26 on iPhone Feature

Here's When iOS 26 Rolls Out Today in Every Time Zone [Update: Out Now!]

Monday September 15, 2025 12:00 am PDT by
Update 10:06 a.m.: iOS 26 is rolling out now, though it may take a bit for all users to see it, so keep checking! Today's the day! Apple is about to release iOS 26, which will deliver the biggest redesign since iOS 7 and bring a range of new features and improvements to iPhones worldwide. It's Apple's biggest software update of the year, and Apple announced at last week's iPhone event that...
Tim Cook Rainbow

Apple Reportedly Plans to Launch These 10 Products in 'Coming Months'

Sunday September 14, 2025 8:45 am PDT by
Apple's annual September event is now in the rearview mirror, with the iPhone 17, iPhone 17 Pro, iPhone 17 Pro Max, iPhone Air, Apple Watch Series 11, Apple Watch Ultra 3, Apple Watch SE 3, and AirPods Pro 3 set to launch this Friday, September 19. As always, there is more to come. In his Power On newsletter today, Bloomberg's Mark Gurman said Apple plans to release many products in the...
iOS 26 Battery Glass Feature

Apple Says Installing iOS 26 Might Impact Battery Life

Monday September 15, 2025 10:56 am PDT by
In the iOS 26 release notes, Apple is warning iPhone users that installing the new software might have a temporary impact on battery life, which is normal. A new support document explains that major iOS updates require background setup like indexing data and files for search, downloading new assets, and updating apps. Further, Apple says that new features could require more resources,...
apple n1 chip

Apple's New N1 Chip in iPhone 17, iPhone 17 Pro, and iPhone Air Has a Wi-Fi 7 Limitation

Saturday September 13, 2025 10:01 am PDT by
The latest iPhone 17, iPhone 17 Pro, iPhone 17 Pro Max, and iPhone Air models are equipped with Apple's all-new N1 chip for Wi-Fi 7, Bluetooth 6, and Thread connectivity. However, the chip has a Wi-Fi 7 bandwidth limitation. According to FCC documents reviewed by MacRumors, the N1 chip in all of the new iPhone models supports up to 160 MHz channel bandwidth for Wi-Fi 7, short of the...
iphone 17 lineup

iPhone 17 Models Launch on September 19 With These New Features

Friday September 12, 2025 7:58 am PDT by
Apple will launch its new iPhone 17 lineup and ultra-thin iPhone Air in stores on Friday, September 19, and the company has already shown off the new devices at its fall event, which ran with the the tagline "Awe dropping." The iPhone 17 series brings a host of new features and enhancements. Here's a rundown of the biggest upgrades and changes: iPhone 17 Display Changes The iPhone...
iphone air all colors

iPhone Air and iPhone 17 Pro Now Facing Extended Delivery Estimates

Saturday September 13, 2025 11:43 am PDT by
iPhone 17, iPhone 17 Pro, iPhone 17 Pro Max, and iPhone Air pre-orders began on Friday in the U.S. and many other countries. iPhone 17 Pro Max delivery estimates quickly slipped beyond the Friday, September 19 launch day for those who had yet to place an order, and now the rest of the new models have started to follow suit. As of shortly after 11:30 a.m. Pacific Time today, select iPhone 17, ...
iPhone 17 Pro Air Boxes

iPhone Air and iPhone 17 Pro Boxes Revealed

Sunday September 14, 2025 1:36 pm PDT by
T-Mobile President Jon Freier today shared real-world photos of Apple's boxes for the iPhone Air, iPhone 17 Pro, and iPhone 17 models, which launch on Friday. Image Credit: Jon Freier Apple has typically included iPhone box renders in its product environmental reports, but it did not do so for the latest models. However, Apple's iPhone Upgrade Program page does offer some images of the boxes, ...
AirPods Pro Firmware Feature

AirPods Pro 2 and AirPods 4 Get iOS 26 Features With New Firmware Update

Monday September 15, 2025 10:50 am PDT by
Apple today released updated firmware for the AirPods Pro 2 and the AirPods 4, introducing support for the new AirPods features that are included in iOS 26, iPadOS 26, and macOS Tahoe. The firmware has a build number of 8A356, and it replaces the current 7E93 firmware. With Apple's new software updates, the AirPods Pro 2 and the AirPods 4 support better audio quality for phone calls and...

Top Rated Comments

cmaier Avatar
56 months ago

What we would like to get: correctly working gmail with most of its features in the native mail app
What we are getting:
Who is “we?” People who don’t care about their privacy, who demand that Apple support non-standards based protocols and functionality, and who work at Google?
Score: 24 Votes (Like | Disagree)
countryside Avatar
56 months ago
Can someone make an extension that lets us schedule a time for an email to be sent?
Score: 21 Votes (Like | Disagree)
kc9hzn Avatar
56 months ago

What we would like to get: correctly working gmail with most of its features in the native mail app
What we are getting:
To be fair, that’s mostly the fault of Google’s bizarre non-standard implementation of IMAP. Those features don’t really work on any app other than GMail.

As for the mail plug-ins, they were never a great solution. Apple will continually move away from systems like mail plug-ins that live in the memory space of another application to inter-application communication systems like extensions that allow an application to extend another application visually without sharing memory space MacOS Classic style. I, for one, am looking forward to having a mail extension system that provides a stable API and that doesn’t break with each point release.
Score: 13 Votes (Like | Disagree)
Peepo Avatar
56 months ago
Hope will be possible to tag a sender as not junk.
Score: 10 Votes (Like | Disagree)
kc9hzn Avatar
56 months ago

Same thing, different day, Apple can never find the original team that built a program, so they have to rebuild it from the ground up! lol
You do realize that Mail.app is a direct continuation of the NeXTStep Mail.app, yes? Which means that it’s nearly 40 years old. Most of the original team is probably retired by now.

But this is also a change that needed to occur. Previously, mail bundles would break between point releases. Not major releases, mere patches. Every time Mail.app got updated, these bundles needed to get updated, too, and, until they did, the bundles wouldn’t work. Now we have a stable API guaranteed not to break on point releases and that will likely be stable across multiple major releases. We’ll probably see more mail extensions as a result of this, while previously, it was only worth the effort to devs who were absolutely serious about email extensibility. This API could also be ported to MobileMail.app, which, until now, hasn’t had any extensibility (except maybe for jailbreaking, but even then, I don’t think Mail was a common target for jailbreakers looking to tweak the system).
Score: 6 Votes (Like | Disagree)
Graham King Avatar
56 months ago
It would be nice to be able to easily add HTML signatures. I might switch back from Spark if this is possible.
Score: 4 Votes (Like | Disagree)