Alex Guyot, writing for MacStories, on the confused behaviour of
mailto links after deleting the Mail app:
First beta and all that of course, but this isn’t a great user experience at all. I honestly can’t think of any way to rectify this besides either not allowing the Mail app to be deleted in the first place, or allowing the user to pick a different default app that will handle mailto: links in the absence of Mail.
A potentially elegant way of handling this would be to allow third-party apps to add
mailto as one of their supported URL protocols. However, that would likely require the ability to select an app to handle them by default when many are installed.
My guess is that Mail will simply be disallowed from being deleted until this can be resolved, however. If it isn’t it’s going to be important for third-party email clients to have a sharing extension — many still do not.