SMTP SASL SASL AUTH PLAIN connection re-use RFC4616 RFC4954 # # Server-side AUTH PLAIN REPLY AUTH 334 PLAIN supported REPLY dXNlci5vbmUAdXNlci5vbmUAc2VjcmV0 235 Authenticated REPLY dXNlci50d28AdXNlci50d28Ac2VjcmV0 235 Authenticated # # Client-side smtp SMTP multiple connection authentication mail body smtp://%HOSTIP:%SMTPPORT/938001 --mail-rcpt recipient@example.com --mail-from sender@example.com -u user.one:secret -T log/upload938 -: smtp://%HOSTIP:%SMTPPORT/938002 --mail-rcpt recipient@example.com --mail-from sender@example.com -u user.two:secret -T log/upload938 # # Verify data after the test has been "shot" EHLO 938001 AUTH PLAIN dXNlci5vbmUAdXNlci5vbmUAc2VjcmV0 MAIL FROM: RCPT TO: DATA QUIT EHLO 938002 AUTH PLAIN dXNlci50d28AdXNlci50d28Ac2VjcmV0 MAIL FROM: RCPT TO: DATA QUIT mail body .