Legacy Outlook vs. New Outlook
SpamSieve has worked with Microsoft Outlook and its predecessors since its inception. This was possible because of their strong support for AppleScript. This macOS technology let SpamSieve access the contents of your e-mail messages, so it could determine whether they were spam, and it also let SpamSieve tell Outlook to move the spam ones to the Junk Email folder.
In October 2020, Microsoft introduced a new version of Outlook built on Web technologies. Many popular features were missing, including AppleScript and rules. Microsoft said that it would continue to support both the current and new versions of Outlook, as separate modes within the same app, while it worked on bringing the new version up to feature parity. Initially, there was a switch to let you opt in to preview the “New Look” version. In recent years, the new version was the default and there was a switch to go back to “Legacy Outlook.” Running in legacy mode has been required for compatibility with SpamSieve since the new mode has not yet restored AppleScript support (nor added another mechanism to provide equivalent functionality).
Ending Support for Legacy Outlook
Microsoft has announced that, as of November 1, 2025, it is ending support for Legacy Outlook. Although we had repeatedly been told that this would not happen until after AppleScript support had been restored, Microsoft is now saying that Legacy Outlook will be discontinued first. When you launch Outlook on your Mac in November, it will force you to migrate to New Outlook. This means that, for a time, most users will not be able to directly use SpamSieve with Outlook.
Which Outlook Versions Are Affected?
Microsoft’s support page says that Legacy Outlook will no longer be supported for Microsoft 365 subscriptions (personal, family, business, and enterprise) or for standalone version of Outlook 2024. If you purchased Outlook LTSC (Office Long Term Service Channel), support will continue until October 2029. We believe, but cannot guarantee, that older versions of Outlook such as 14.x and possibly early versions of 15.x from before Outlook was subscription-based may continue to work. As of this writing, the current version of Outlook is 16.100.2, which includes the switch for changing between Legacy Outlook and New Outlook. However, Microsoft has said that, even if you keep this version installed and don’t update it, the legacy mode will stop working on November 1, even if you have an active Microsoft 365 subscription.
Why Did My Legacy Outlook Stop Working Early?
The version of Outlook distributed by Microsoft is managed by the Microsoft AutoUpdate app. If you have Microsoft AutoUpdate’s Update Channel set to Current Channel (Preview) or to the beta channel, it will download and install new versions of Outlook before they are released to the general public. As of this writing, the preview version of Outlook is 16.100.3, which claims to still support Legacy Outlook, but the switch to enable it doesn’t work. To restore support, you can go back to version 16.100.2 by downloading it from the Mac App Store or by logging into your Microsoft account, clicking on View all subscriptions, and then clicking Install desktop versions of Microsoft 365 apps like Word, Excel, and PowerPoint to your device.
How Can I Continue Using SpamSieve?
With other popular features such as rules also not available with New Outlook, we expect that some customers may choose to switch to another mail client. There are a variety of Mac e-mail apps that work with SpamSieve.
If you’d like to continue using New Outlook, you can still use SpamSieve to filter your Outlook e-mail even though SpamSieve will no longer be able to directly communicate with Outlook. All Macs include Apple’s Mail app, and it works great with SpamSieve. If you add your mail accounts to Apple Mail and set up SpamSieve for Apple Mail, SpamSieve and Mail will filter your inbox, and the spam messages will automatically be removed from your Outlook inbox, too. You can hide Mail or run it without any windows open so that the filtering happens invisibly in the background (though you’ll need to remember to launch Mail when you restart your Mac). You do not have retrain SpamSieve from scratch; it will keep using the same training data from when you were using it with Outlook. Going forward, if you need to correct any filtering mistakes you can train SpamSieve directly from Outlook by moving messages into the special TrainSpam or TrainGood mailbox. To do this, first make sure that Train messages in TrainSpam and TrainGood is selected in the Settings ‣ Apple Mail ‣ Training window. There’s more information about how this works in the Drone Setup and Remote Training section of the manual.
When Will SpamSieve Work Directly With Outlook Again?
Microsoft’s roadmap currently has AppleScript support expected to roll out in December 2025. At that time, the current version of SpamSieve may automatically start working with Outlook again. We will test with beta versions of Outlook as they become available and update SpamSieve as necessary.
Support for rules is also not implemented yet, and it is not currently on Microsoft’s roadmap, but this is not required for SpamSieve support. Legacy Outlook had a performance bug that required a different SpamSieve setup if you had a large number of messages in your inbox, and in some cases this required using Outlook’s rules feature. It’s unclear what the performance characteristics of New Outlook’s AppleScript support will be and, thus, whether rules support will be required for large inboxes. Many mail providers support server-side rules, which is good enough for SpamSieve’s purposes.
You can choose Give Feedback from the Help menu in Outlook to ask Microsoft to prioritize support for AppleScript, rules, or any other features that you miss.