I unearthed an MS account and tried to get some debug. The issue seems to be the return of the browser auth to k9 with a intent that contains the auth (“dat=msauth://com.fsck.k9/…”)
E App : failed to start third party app activity
E App : android.content.ActivityNotFoundException: No Activity found to handle Intent { act=android.intent.action.VIEW cat=[android.intent.category.BROWSABLE] dat=msauth://com.fsck.k9/Dx8yUsuhyU3dYYba1aA16Wxu5eM=?code=hunter2 flg=0x10000000 (has extras) }
E App : at android.app.Instrumentation.checkStartActivityResult(Instrumentation.java:2071)
k9 is registering for that intent at https://github.com/thundernest/k-9/commit/598a1714645f49393ebc47f602c73d94f1eb730c#diff-81a6b9bb5c611adff17d82e07aedd503b429601629b51532e950e4b80d8c6348
so my wild guess - not familiar with Android appdev much, the Manifest uses the appid as variable at
<data android:scheme="msauth" android:host="${applicationId}"/>
and I wonder if this collides with the appid customization to foundation.e.mail at app/k9mail/build.gradle · a59f9b37 · e / os / Mail · GitLab
as the scheme the mail intent is listening for dat://foundation.e.mail/… but mail emits the k9 appid host.
So I guess the constant OAUTH_MICROSOFT_REDIRECT_URI at app/k9mail/build.gradle · a59f9b37 · e / os / Mail · GitLab needs to be adjusted
Edit: filed at Mail and microsoft Oauth2: No Activity found to handle Intent (#6198) · Issues · e / Backlog · GitLab