SMTP SASL SASL AUTH DIGEST-MD5 SASL AUTH PLAIN SASL DOWNGRADE RFC2831 RFC4954 # # Server-side AUTH DIGEST-MD5 PLAIN REPLY "AUTH DIGEST-MD5" 334 Rubbish REPLY * 501 AUTH exchange cancelled by client REPLY "AUTH PLAIN" 334 PLAIN supported REPLY dXNlcgB1c2VyAHNlY3JldA== 235 Authenticated # # Client-side smtp debug crypto SMTP DIGEST-MD5 authentication with SASL downgrade mail body smtp://%HOSTIP:%SMTPPORT/937 --mail-rcpt recipient@example.com --mail-from sender@example.com -u user:secret -T - # # Verify data after the test has been "shot" EHLO 937 AUTH DIGEST-MD5 * AUTH PLAIN dXNlcgB1c2VyAHNlY3JldA== MAIL FROM: RCPT TO: DATA QUIT mail body .