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 (OAUTHBEARER) authentication 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 %b64[n,a=user,%01host=127.0.0.1%01port=%SMTPPORT%01auth=Bearer mF_9.B5f-4.1JqM%01%01]b64% MAIL FROM: RCPT TO: DATA QUIT mail body .