By default, protocols such as HTTP (web service), SMTP (mail sending service), IMAP/POP3 (mail receiving service), LDAP etc. send packets in plain text format.
SSL (Secure Socket Layer) is helpful in encrypting the communication among servers or between server and client.
This system is primarily addressed for those servers which want to use encrypted communication, but not in public internet.
for getting your certificate signed or making your department a secondary CA.