In cryptography, CRAM-MD5 is a challenge-response authentication mechanism (hence "CRAM") defined in RFC 2195 based on the HMAC-MD5 MAC algorithm. It is employed by some SASL implementations, and it is quite often supported by SMTP-AUTH Mail submission agents.

Read more about CRAM-MD5:  Protocol, Protocol Weaknesses, History

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CRAM-MD5 - History
... CRAM-MD5 was originally defined in RFC 2095, later rendered obsolete by RFC 2195 ... CRAM-MD5 is required for On-Demand Mail Relay (ODMR) defined in RFC 2645 ... (IANA) maintains two registries relevant for CRAM-MD5 SASL-mechanisms incl ...