CRAM-MD5 is a method of encryption that can be used by Mail when logging in to SMTP and IMAP servers in Mac OS X 10.1.2 and later. CRAM-MD5 is used by default to encrypt your password when sending mail using an SMTP server or checking mail on an IMAP server. If the server does not have a CRAM-MD5 encrypted authentication feature, Mail reverts to sending your password in clear text.
Note: In rare cases, Mail may not communicate with a server that responds unexpectedly to CRAM-MD5 encrypted authentication. In this case, Mail will generate a message that can be viewed in the Console application. The message has this format:
date&time Mail [process id] CRAM-MD5 authentication failed for <SMTP or IMAP> account username@server
In this case, CRAM-MD5 authentication may be manually disabled by following these steps:
1. Open the Terminal application.
2. Type this line exactly:
defaults write com.apple.mail DisableMD5Authentication YES
3. Press Return.
To re-enable CRAM-MD5 authentication, follow the above directions, but type the command:
defaults write com.apple.mail DisableMD5Authentication NO