+Exim version 4.64
+-----------------
+
+1. Callouts were setting the name used for EHLO/HELO from $smtp_active_
+hostname. This is wrong, because it relates to the incoming message (and
+probably the interface on which it is arriving) and not to the outgoing
+callout (which could be using a different interface). This has been
+changed to use the value of the helo_data option from the smtp transport
+instead - this is what is used when a message is actually being sent. If
+there is no remote transport (possible with a router that sets up host
+addresses), $smtp_active_hostname is used. This change is mentioned here in
+case somebody is relying on the use of $smtp_active_hostname.
+
+2. A bug has been fixed that might just possibly be something that is relied on
+in some configurations. In expansion items such as ${if >{xxx}{yyy}...} an
+empty string (that is {}) was being interpreted as if it was {0} and therefore
+treated as the number zero. From release 4.64, such strings cause an error
+because a decimal number, possibly followed by K or M, is required (as has
+always been documented).
+
+3. There has been a change to the GnuTLS support (ChangeLog/PH/20) to improve
+Exim's performance. Unfortunately, this has the side effect of being slightly
+non-upwards compatible for versions 4.50 and earlier. If you are upgrading from
+one of these earlier versions and you use GnuTLS, you must remove the file
+called gnutls-params in Exim's spool directory. If you don't do this, you will
+see this error:
+
+ TLS error on connection from ... (DH params import): Base64 decoding error.
+
+Removing the file causes Exim to recompute the relevant encryption parameters
+and cache them in the new format that was introduced for release 4.51 (May
+2005). If you are upgrading from release 4.51 or later, there should be no
+problem.
+
+