Hi,

In case a single CURLOPT_MAILAUTH 'bitmasked' option is favoured
relevant bits in curl.h could be something like the following, in
which lower bits are used for authentication mechanisms and higher
bits for parametrization purposes. Bits in between free for future
expansion.

#define CURLMAIL_AUTH_LOGIN (1<<0)
#define CURLMAIL_AUTH_PLAIN (1<<1)
#define CURLMAIL_AUTH_CRAM_MD5 (1<<2)
#define CURLMAIL_AUTH_DIGEST_MD5 (1<<3)
#define CURLMAIL_AUTH_GSSAPI (1<<4)
#define CURLMAIL_AUTH_EXTERNAL (1<<5)
#define CURLMAIL_AUTH_NTLM (1<<6)

#define CURLMAIL_AUTH_ANY ((1<<0) & (1<<1) & (1<<2) & (1<<3) & \
                                  (1<<4) & (1<<5) & (1<<6))

#define CURLMAIL_AUTH_NO_IR (1<<31)

Obviously CURLMAIL_AUTH_NO_IR is the relevant bit to disable sending
client initial response in AUTH command.

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