a0 NOOP See test/config/oauth2/Caddyfile to generate the below XOAUTH2 string
a1 AUTHENTICATE XOAUTH2 dXNlcj11c2VyMUBsb2NhbGhvc3QubG9jYWxkb21haW4BYXV0aD1CZWFyZXIgRE1TX1lXTmpaWE56WDNSdmEyVnUBAQ==
a2 EXAMINE INBOX
a3 LOGOUT