What is Mesyx?
Mesyx is a Message and Data Exchange, it allows one to send, receive and relay messages to other parties.
It accepts standard cleartext or PGP-encrypted emails over SMTP and can relay these again to other SMTP servers. Or, the party trick: it can store these encrypted as Mesyx blobs. This thus allows interaction with the standard email system worldwide, while slowly upgrading to Mesyx everywhere.
Access to the stored data happens using Mesyx client, which can expose itself as a IMAP server, thus allowing any standard email client access.
Plainly said: Mesyx is secured messaging done properly.