There is some potentially important news regarding the email client pre-installed in the new version of macOS, Sonoma: it has been confirmed that the legacy plugins, developed before the advent of MailKit, will no longer be supported. Already during the presentation of MailKit, in 2021 with the release of Monterey, Apple had warned that this would happen, but had not indicated any precise timing and modality.
The confirmation comes from the AltStore developers, an alternative app store for iPhones and iPads without jailbreak, which cite an official statement by Apple employees during the in-depth sessions at WWDC 2023. This will also have an impact on the AltStore software proposal itself: the service is in fact based on a companion app, known as AltServer, which needs to be installed on a computer running macOS or Windows. With the advent of Sonoma, the AltServer plugin for the Mac mail client will no longer be compatible. However, the developers have stated that they are working on a new distribution method.
PSA: Confirmed in WWDC labs that legacy Mail plug-ins are NOT supported on macOS Sonoma. MailKit-based extensions are the only supported method going forward.
AltServer’s Mail plug-in will no longer work once you update, but we’re working on a new method we hope to release soon.
— AltStore.io (@altstoreio) June 14, 2023
Unfortunately not always plugins can be adapted to MailKit: they are more modern and secure APIs, but inevitably have more restrictions and limitations than the previous methodology (interesting to note that this is also reflected in the terminology adopted to define them, from “plugins” to “extensions”). Apple’s decision is already effective with the first Beta of Sonoma, released close to the opening keynote of WWDC a few days ago.
