SMTP SASL SASL AUTH OAUTH2 SASL-IR RFC4954 RFC6749 RFC7628 # # Server-side AUTH OAUTHBEARER REPLY AUTH 235 Authenticated # # Client-side smtp SMTP OAuth 2.0 authentication (OAUTHBEARER) with initial response mail body smtp://%HOSTIP:%SMTPPORT/947 --mail-rcpt recipient@example.com --mail-from sender@example.com -u user --oauth2-bearer mF_9.B5f-4.1JqM --sasl-ir -T - # # Verify data after the test has been "shot" EHLO 947 AUTH OAUTHBEARER dXNlcj11c2VyAWhvc3Q9MTI3LjAuMC4xAXBvcnQ9OTAwNQFhdXRoPUJlYXJlciBtRl85LkI1Zi00LjFKcU0BAQ== MAIL FROM: RCPT TO: DATA QUIT mail body .