Upon receipt of a correctly formatted XCLIENT command, the
server resets state to the initial SMTP greeting protocol stage.
Depending on the outcome of optional access decisions, the server
responds with 220 or with a suitable rejection code.
For practical reasons it is not always possible to reset the
complete server state to the initial SMTP greeting protocol stage:
-
TLS session information may not be reset, because turning off
TLS leaves the connection in an undefined state. Consequently, the
server may not announce STARTTLS when TLS is already active, and
access decisions may be influenced by client certificate information
that was received prior to the XCLIENT command.
-
The SMTP server must not reset attributes that were received
with the last XCLIENT command. This includes HELO or PROTO attributes.
NOTE: Postfix implementations prior to version 2.3 do not jump
back to the initial SMTP greeting protocol stage. These older
implementations will not correctly simulate connection-level access
decisions under some conditions.
