4.6.1 Turning Off New Outlook

As of September 2025, the Microsoft Outlook app can run in two modes: Legacy Outlook and New Outlook. SpamSieve uses AppleScript to communicate with Outlook, which is currently only supported in the legacy mode. Microsoft is ending support for Legacy Outlook on November 1, 2025. There’s more information about this, and how it affects SpamSieve, in the End of Support for Legacy Outlook section of the manual.

To switch to legacy mode, in Outlook, click on the Outlook menu at the top of the screen and make sure that Legacy Outlook is checked or that New Outlook is unchecked:

outlook new outlook

In some versions of Outlook, there is no switch to turn off “New Outlook” once it is enabled, but you can do so by entering this command in the Terminal app:

defaults write com.microsoft.Outlook IsRunningNewOutlook NO

and pressing Return. In some cases you may instead need this command:

defaults write com.microsoft.Outlook EnableNewOutlook NO

Note that the old and new versions of Outlook have separate mail storage. Messages stored in On My Computer folders will not automatically sync between the two versions.