SMTP SASL SASL AUTH EXTERNAL SASL-IR RFC4422 RFC4954 # # Server-side AUTH EXTERNAL REPLY AUTH 235 Authenticated # # Client-side smtp SMTP external authentication with initial response without credentials mail body 'smtp://;AUTH=EXTERNAL@%HOSTIP:%SMTPPORT/945' --mail-rcpt recipient@example.com --mail-from sender@example.com --sasl-ir -T - # # Verify data after the test has been "shot" EHLO 945 AUTH EXTERNAL = MAIL FROM: RCPT TO: DATA QUIT mail body .