Yes, email2 is very secure!
email2 secures the channel itself by rerouting all sensitive data across HTTPS connections instead of the less secure, standard SMTP/POP3/IMAP4 connections. PKI secures the message by encrypting it (one way only) and then sending it across the less secure basic email channels.
With email2, messages are stored in a centralized, secure message repository (your PEN). Access to email2 messages is only granted to authorized users with sufficient privileges.
In addition, email2 doesn't have to replace PKI - both can work flawlessly in conjunction with one another. Neither the security of email2 nor PKI is compromised.
// Edited July 2008