SMTP SMTP AUTH PLAIN RFC4616 RFC4954 # # Server-side AUTH PLAIN REPLY AUTH 334 PLAIN supported REPLY dGVzdAB0ZXN0ADEyMzQ= 235 Authenticated # # Client-side smtp SMTP plain authentication mail body smtp://%HOSTIP:%SMTPPORT/903 --mail-rcpt recipient@example.com --mail-from sender@example.com -u test:1234 -T - # # Verify data after the test has been "shot" EHLO 903 AUTH PLAIN dGVzdAB0ZXN0ADEyMzQ= MAIL FROM: RCPT TO: DATA QUIT mail body .