E-mail encryption with mailbox.org Guard is 100% compatible with the OpenPGP Standard.

The web interface of mailbox.org allows the sending, receiving, signing, and verification of PGP/MIME- and PGP/Inline-encrypted e-mails. Users of mailbox.org can thus communicate securely with everyone else who uses a PGP-compatible e-mail client or -plugin.

As of now ECC (Elliptical Curve Cryptology) keys according to RFC 6637 are not supported.