Steve on 13 Jun, 2019 10:11 PM
thanks for taking the time to report this problem.
We are aware of macOS 10.15 Catalina developer releases. The fact that GPG Mail will not work until there is an official release is expected. We connected this discussion with the corresponding ticket and will let you know as soon as we have a version ready for testing.
Following is an explanation of why GPG Mail is rendered incompatible after macOS updates:
While a new major version of Mail.app may introduce only minor visual changes, the codebase underneath it changes dramatically. Other Mail applications provide a number of functions, plugin developers can leverage to extend the application. These functions are guaranteed not to be changed or if they are, developers are notified in advance in order to adapt their plugins to the changes. This however is not the case for Mail.app. Apple can and does change everything they want whenever they want to. There's no notification of what has changed whatsoever, not even for the developers of the most popular Mail plugins.
Especially during the beta phase of new major versions of macOS, Apple usually introduces a slew of major internal changes with each beta. So in the worst case, plugin developers have to reverse engineer Mail again and again in order to find new or modified functions they could use to enhance Mail the way they need to. In the worst case, those changes can require us to re-reverse engineer most of Mail.app and rewrite a whole lot of code. Other developers might not be as strongly affected by the changes, since it heavily depends on the Mail functions previously relied upon by each plugin.
It's hard to tell when there will be an official (beta) release of GPG Mail for macOS Catalina.
We suggest to get in touch with Apple about this via their feedback form. An example where Apple changes in Mail broke GPG Mail was macOS 10.13.2b3. Apple fixed things around S/MIME and, while doing that, changed some classes. GPG Mail thus no longer worked as expected. With no API this means, we had to invest plenty of time to reverse engineer those changes.