Hello, thank you for your reply.
Edit → Preferences → Choose the account → Edit → Security → Check "Always trust keys in my keyring when encrypting"
That's easier than I thought it would be. It works now without problems.
I would have expected you to get that verbose message in the yellow error box, instead of needing to use strace in order to find it, though.
Yes, that would have made this whole thing much easier. But anyway, thank you all :) Best regards, Tim Rausch
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