SASL

• RFC 4422 Simple Authentication and Security Layer (SASL)
• RFC 2195 IMAP/POP AUTHorize Extension for Simple Challenge/Response (CRAM-MD5)
• RFC 2595 Using TLS with IMAP, POP3 and ACAP (PLAIN)

Google TalkはSASL PLAINのみ対応、ただしstarttls必須だそうな。