I receive this error when trying to update:
W: GPG error: http://download.bareos.org Release: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A59EFE1D5A01E889
Normally I just add the key from MIT's server:
gpg --keyserver pgpkeys.mit.edu --recv-key A59EFE1D5A01E889
gpg -a --export A59EFE1D5A01E889 | apt-key add -
However, this key is not published in MIT's server.
Sitz der Gesellschaft: Köln | Amtsgericht Köln: HRA 29646
Komplementär: Bareos Verwaltungs-GmbH
Geschäftsführer: S. Dühr, M. Außendorf,
J. Steffens, Philipp Storz, M. v. Wieringen