+PH/05 The "control=freeze" ACL modifier can now be followed by /no_tell. If
+ the global option freeze_tell is set, it is ignored for the current
+ message (that is, nobody is told about the freezing), provided all the
+ "control=freeze" modifiers that are obeyed in the current message have
+ the /no_tell option.
+
+PH/06 In both GnuTLS and OpenSSL, an expansion of tls_privatekey that results
+ in an empty string is now treated as unset.
+
+PH/07 There is a new log selector called sender_verify_fail, which is set by
+ default. If it is unset, the separate log line that gives details of a
+ sender verification failure is not written. Log lines for the rejection
+ of SMTP commands (e.g. RCPT) contain just "sender verify failed", so some
+ detail is lost.
+
+PH/08 The default for dns_check_names_pattern now allows slashes within names,
+ as there are now some PTR records that contain slashes. This check is
+ only to protect against broken name servers that fall over on strange
+ characters, so the fact that it applies to all lookups doesn't matter.
+
+PH/09 The default for rfc4131_query_timeout has been changed from 30s to 5s.
+
+PH/10 When compiled on FreeBSD, NetBSD, or BSD/OS, the pipe transport has a new
+ Boolean option called use_classresources, defaulting false. If it is set
+ true, the setclassresources() function is used to set resource limits
+ when a pipe transport is run to perform a delivery. The limits for the
+ uid under which the pipe is to run are obtained from the login class
+ database.
+
+PH/11 If retry_interval_max is set greater than 24 hours, it is quietly reset
+ to 24 hours. This avoids potential overflow problems when processing G
+ and H retry rules, and it seems reasonable to require a retry at least
+ once a day.
+
+PH/12 When the plaintext authenticator is running as a client, the server
+ challenges are now checked to ensure they are valid base64 strings. The
+ default action on failure is to abort the authentication. However, if
+ client_ignore_invalid_base64 is set true, invalid responses are ignored.
+
+PH/13 When the plaintext authenticator is running as a client, the challenges
+ from the server are placed in $auth1, $auth2, etc. as they are received.
+ Thus, the challege that is received in response to sending the first
+ string (with the AUTH command) can be used in the expansion of the second
+ string, and so on. Currently, up to 3 challenge strings are available in
+ this way. If an invalid base64 string is received when client_ignore_
+ invalid_base64 is set, an empty string is put in the $auth<n> variable.
+
+PH/14 Messages created by the autoreply transport now contain a References:
+ header. This is constructed in accordance with rules that are described
+ in section 3.64 of RFC 2822, which states that replies should contain
+ such a header line, and section 3.14 of RFC 3834, which states that
+ automatic responses are not different in this respect. However, because
+ some mail processing software does not cope well with very long header
+ lines, no more than 12 message IDs are copied from the References: header
+ line in the incoming message. If there are more than 12, the first one
+ and then the final 11 are copied, before adding the message ID of the
+ incoming message.
+