STARTTLS is an extension to plain text communication protocols, which offers a way to upgrade a plain text connection to an encrypted (TLS or SSL) connection instead of using a separate port for encrypted communication.STARTTLS for IMAP and POP3 is defined in RFC 2595, for SMTP in RFC 3207, for XMPP in RFC 6120, for LDAP in RFC 2830, for NNTP in RFC 4642, and for FTP in RFC 4217. For IRC, the de facto definition is documented at the InspIRCd wiki.