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

15 New Things Your iPhone Can Do in iOS 26.2

Friday December 5, 2025 9:40 am PST by
Apple is about to release iOS 26.2, the second major point update for iPhones since iOS 26 was rolled out in September, and there are at least 15 notable changes and improvements worth checking out. We've rounded them up below. Apple is expected to roll out iOS 26.2 to compatible devices sometime between December 8 and December 16. When the update drops, you can check Apple's servers for the ...
Intel Inside iPhone Feature

Apple's Return to Intel Rumored to Extend to iPhone

Friday December 5, 2025 10:08 am PST by
Intel is expected to begin supplying some Mac and iPad chips in a few years, and the latest rumor claims the partnership might extend to the iPhone. In a research note with investment firm GF Securities this week, obtained by MacRumors, analyst Jeff Pu said he and his colleagues "now expect" Intel to reach a supply deal with Apple for at least some non-pro iPhone chips starting in 2028....
ive and altman

Jony Ive's OpenAI Device Barred From Using 'io' Name

Friday December 5, 2025 6:22 am PST by
A U.S. appeals court has upheld a temporary restraining order that prevents OpenAI and Jony Ive's new hardware venture from using the name "io" for products similar to those planned by AI audio startup iyO, Bloomberg Law reports. iyO sued OpenAI earlier this year after the latter announced its partnership with Ive's new firm, arguing that OpenAI's planned "io" branding was too close to its...
iPhone 17 Pro Cosmic Orange

10 Reasons to Wait for Next Year's iPhone 18 Pro

Monday December 1, 2025 2:40 am PST by
Apple's iPhone development roadmap runs several years into the future and the company is continually working with suppliers on several successive iPhone models at the same time, which is why we often get rumored features months ahead of launch. The iPhone 18 series is no different, and we already have a good idea of what to expect for the iPhone 18 Pro and iPhone 18 Pro Max. One thing worth...
Photos App Icon Liquid Glass

John Gruber Shares Scathing Commentary About Apple's Departing Software Design Chief

Thursday December 4, 2025 9:30 am PST by
In a statement shared with Bloomberg on Wednesday, Apple confirmed that its software design chief Alan Dye will be leaving. Apple said Dye will be succeeded by Stephen Lemay, who has been a software designer at the company since 1999. Meta CEO Mark Zuckerberg announced that Dye will lead a new creative studio within the company's AR/VR division Reality Labs. On his blog Daring Fireball,...
Apple John Ternus 2019

Will John Ternus Really Be Apple's Next CEO?

Friday December 5, 2025 9:01 am PST by
There is uncertainty about Apple's head of hardware engineering John Ternus succeeding Tim Cook as CEO, The Information reports. Some former Apple executives apparently hope that a new "dark-horse" candidate will emerge. Ternus is considered to be the most likely candidate to succeed Cook as CEO. The report notes that he is more likely to become CEO than software head chief Craig Federighi, ...
maxresdefault

iPhone Fold: Launch, Pricing, and What to Expect From Apple's Foldable

Monday December 1, 2025 3:00 am PST by
Apple is expected to launch a new foldable iPhone next year, based on multiple rumors and credible sources. The long-awaited device has been rumored for years now, but signs increasingly suggest that 2026 could indeed be the year that Apple releases its first foldable device. Subscribe to the MacRumors YouTube channel for more videos. Below, we've collated an updated set of key details that ...
ios 18 to ios 26 upgrade

Apple Pushes iPhone Users Still on iOS 18 to Upgrade to iOS 26

Tuesday December 2, 2025 11:09 am PST by
Apple is encouraging iPhone users who are still running iOS 18 to upgrade to iOS 26 by making the iOS 26 software upgrade option more prominent. Since iOS 26 launched in September, it has been displayed as an optional upgrade at the bottom of the Software Update interface in the Settings app. iOS 18 has been the default operating system option, and users running iOS 18 have seen iOS 18...
iOS 26

Apple Seeds iOS 26.2 and iPadOS 26.2 Release Candidates to Developers and Public Beta Testers

Wednesday December 3, 2025 10:33 am PST by
Apple today seeded the release candidate versions of upcoming iOS 26.2 and iPadOS 26.2 updates to developers and public beta testers, with the software coming two weeks after Apple seeded the third betas. The release candidates represent the final versions of iOS 26.2 and iPadOS 26.2 that will be provided to the public if no further bugs are found during this final week of testing....
Touchscreen MacBook Feature

Here Are the Four MacBooks Apple Is Expected to Launch Next Year

Monday December 1, 2025 5:00 am PST by
2026 could be a bumper year for Apple's Mac lineup, with the company expected to announce as many as four separate MacBook launches. Rumors suggest Apple will court both ends of the consumer spectrum, with more affordable options for students and feature-rich premium lines for users that seek the highest specifications from a laptop. Below is a breakdown of what we're expecting over the next ...

Top Rated Comments

cmaier Avatar
59 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
59 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
59 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
59 months ago
Hope will be possible to tag a sender as not junk.
Score: 10 Votes (Like | Disagree)
kc9hzn Avatar
59 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
59 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)