There's an open source (GPL) client app (last updated last week) on F-Droid called Dib2Qm for exactly this, and it's apparently e2e as well. I haven't used it,

There's an open source (GPL) client app (last updated last week) on F-Droid called Dib2Qm for exactly this, and it's apparently e2e as well. I haven't used it, I just happened across it yesterday out of sheer coincidence. Link: https://f-droid.org/en/packages/net.sourceforge.dibdib.android.dib2qm/ https://f-droid.org/en/packages/net.sourceforge.dibdib.andro...