From top of the email, remove everything after
-----BEGIN PGP SIGNED MESSAGE-----
untill the first line change.
For example:
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1
Hi,You would remove
-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1so the message would be
Hi,
Remove everything between lines
-----BEGIN PGP SIGNATURE-----
and
-----END PGP SIGNATURE-----