Email protocols were considered insecure until the introduction of SSL and TLS. The basic protocols (SMTP, POP3 and IMAP4) did not have the mechanism to encrypt and provide data integrity for mail messages between two connections. Initially, SSL was added to email clients and later its successor, the TLS (SSLv3), was added to mail clients as well as to the SMTP protocol.Before the introduction of SSL and TLS, email protocols were considered insecure.
The basic protocols (SMTP, POP, and IMAP) did not have the mechanism to encrypt and provide data integrity for mail messages between two connections. Initially, SSL was added to email clients and later its successor, the TLS (SSLv3), was added to mail clients as well as to the SMTP protocol.