SMTP SMTP AUTH PLAIN RFC4616 RFC4954 # # Server-side REPLY EHLO 250 AUTH PLAIN REPLY AUTH 334 PLAIN supported REPLY dGVzdAB0ZXN0ADEyMzQ= 235 Authenticated # # Client-side smtp SMTP plain authentication mail body smtp://%HOSTIP:%SMTPPORT/user --mail-rcpt 903@foo --mail-from 903@from -u test:1234 -T - # # Verify data after the test has been "shot" EHLO user AUTH PLAIN dGVzdAB0ZXN0ADEyMzQ= MAIL FROM:<903@from> RCPT TO:<903@foo> DATA QUIT mail body .