When processing an email, Wallace forces its encoding to quoted-printable. If the original email had a different encoding, Wallace simply goes ahead and alters the email body.
Obviously, this breaks DKIM and PGP signatures!

See these two recent mailing-list threads:
https://lists.kolab.org/pipermail/users/2018-June/021442.html (DKIM)
https://lists.kolab.org/pipermail/users/2018-June/021445.html (PGP)