What are some alternatives?
When comparing GNUPGK and Zoho Mail, you can also consider the following products
GPG Suite - Use GPG Suite to encrypt, decrypt, sign and verify files or messages.
ProtonMail - Secure email with absolutely no compromises. Get your free encrypted email account today.
GPGTools - Use GPG Suite to encrypt, decrypt, sign and verify files or messages.
Gmail - Gmail is available across all your devices Android, iOS, and desktop devices. Sort, collaborate or call a friend without leaving your inbox.
GnuPG - GnuPG is a complete and free implementation of the OpenPGP standard as defined by RFC4880 (also known as PGP).
FastMail - Email, calendars, and contacts to highest standards of security, privacy and reliability.