SMTP SASL SASL AUTH EXTERNAL RFC4422 RFC4954 # Server-side AUTH EXTERNAL REPLY AUTH 334 EXTERNAL supported REPLY %b64[user]b64% 235 Authenticated # Client-side smtp SMTP external authentication mail body 'smtp://user;AUTH=EXTERNAL@%HOSTIP:%SMTPPORT/%TESTNUMBER' --mail-rcpt recipient@example.com --mail-from sender@example.com -T - # Verify data after the test has been "shot" EHLO %TESTNUMBER AUTH EXTERNAL %b64[user]b64% MAIL FROM:%LTsender@example.com%GT RCPT TO:%LTrecipient@example.com%GT DATA QUIT mail body .