+PH/17 The ACL modifier control=allow_auth_unadvertised can be used to permit a
+ client host to use the SMTP AUTH command even when it has not been
+ advertised in response to EHLO. Furthermore, because there are apparently
+ some really broken clients that do this, Exim will even accept AUTH after
+ HELO when this control is set. It should only be used if you really need
+ it, and you should limit its use to those broken hosts that do not work
+ without it. For example:
+
+ warn hosts = 192.168.34.25
+ control = allow_auth_unadvertised
+
+ This control is permitted only in the connection and HELO ACLs.
+
+PH/18 There is a new ACL modifier called "add_header" which does what its name
+ implies. It specifies one of more header lines that are to be added to an
+ incoming message, assuming, of course, that the message is ultimately
+ accepted.
+
+ This modifier is permitted in the MAIL, RCPT, PREDATA, DATA, MIME, and
+ non-SMTP ACLs (in other words, those that are concerned with accepting a
+ message). Added header lines are accumulated during the MAIL, RCPT, and
+ PREDATA ACLs, with any duplicates being discarded. They are then added to
+ the message before processing the DATA and MIME ACLs, during which
+ further added header lines are accumulated, again with duplicates
+ discarded. Thus, it is possible to add two identical header lines to an
+ SMTP message, but only if one is added before DATA and one after.
+
+ In the case of non-SMTP messages, new headers are accumulated during the
+ non-SMTP ACL, and added to the message at the end.
+
+ The add_header modifier is available for use with all ACL verbs. In the
+ case of the WARN verb, add_header supersedes the use of "message" for
+ this purpose; for the other verbs, it provides a new facility. If both
+ add_header and "message" are present on a WARN verb, both are processed
+ according to their specifications.
+
+ The add_header modifier acts immediately it is encountered during the
+ processing of an ACL. This is different to the (now-deprecated) use of
+ "message" on a WARN verb, where the action is taken only if all the
+ conditions are true. Notice the difference between these two cases on a
+ RCPT ACL:
+
+ deny add_header = ADDED: some text
+ <some condition>
+
+ deny <some condition>
+ add_header = ADDED: some text
+
+ In the first case, the header is always added, whether or not the current
+ recipient is rejected. In the second case, the header is added only if
+ the recipient is rejected.
+
+ If add_header appears more than once on an ACL statement, multiple
+ headers are added, provided that they have different content. (In the
+ case of WARN with "message", only the last value of "message" is used.)
+
+ The facility for specifying where the new header is to be inserted, as
+ described for WARN with "message" in section 39.19 of the 4.60 manual, is
+ supported.
+
+PH/19 The following errors can now be detected in retry rules:
+
+ mail_4xx This is like rcpt_4xx, but applies to MAIL commands
+
+ data_4xx This is like rcpt_4xx, but applies to DATA commands and the
+ response code after the end of the data
+
+ lost_connection This error occurs when the server unexpectedly closes
+ the SMTP connection. There may, of course, legitmate reasons
+ for this (host died, network died), but if it repeats a lot
+ for the same host, it indicates something odd.
+
+ tls_required The server was required to use TLS (hosts_require_tls),
+ but either did not offer it, or responded with 4xx to
+ STARTTLS, or there was a problem setting up the TLS connection
+
+ Note that a 5xx response to STARTTLS is a permanent error.
+
+