SMTP SASL SASL AUTH EXTERNAL RFC4422 RFC4954 # # Server-side AUTH EXTERNAL REPLY AUTH 334 EXTERNAL supported REPLY dXNlcg== 235 Authenticated # # Client-side smtp SMTP external authentication mail body 'smtp://user;AUTH=EXTERNAL@%HOSTIP:%SMTPPORT/950' --mail-rcpt recipient@example.com --mail-from sender@example.com -T - # # Verify data after the test has been "shot" EHLO 950 AUTH EXTERNAL dXNlcg== MAIL FROM: RCPT TO: DATA QUIT mail body .