1. Make sure claws-mail is compile with gpgme support (--enable-gpgme)
2. Load the PGP/Core, PGP/inline and PGP/MIME from the plugins screen...
3. Enable Privacy System with either PGP Inline or PGP MIME. It is optional to enable sign and encrypt email as default.
4. Configure GPG plugins to use the default key or key by your email address
5. Compose an email with sign or encrypt option enable
6. You will prompt for the passphase to decrypt and encrypt any email