TLS SNI support for OpenSSL ($tls_sni)

[exim.git] / doc / doc-docbook / spec.xfpt

diff --git a/doc/doc-docbook/spec.xfpt b/doc/doc-docbook/spec.xfpt
index e719855f8e0dc6e1ff9aac7717d491aa84808ec7..32e24ca8086811f1669b75f8f3c2436f835433f5 100644 (file)
--- a/doc/doc-docbook/spec.xfpt
+++ b/doc/doc-docbook/spec.xfpt
@@ -11888,6 +11888,24 @@ the value of the Distinguished Name of the certificate is made available in the
 value is retained during message delivery, except during outbound SMTP
 deliveries.
 
+.new
+.vitem &$tls_sni$&
+.vindex "&$tls_sni$&"
+.cindex "TLS" "Server Name Indication"
+When a TLS session is being established, if the client sends the Server
+Name Indication extension, the value will be placed in this variable.
+If the variable appears in &%tls_certificate%& then this option and
+&%tls_privatekey%& will be re-expanded early in the TLS session, to permit
+a different certificate to be presented (and optionally a different key to be
+used) to the client, based upon the value of the SNI extension.
+
+The value will be retained for the lifetime of the message, and not changed
+during outbound SMTP.
+
+This is currently only available when using OpenSSL, built with support for
+SNI.
+.wen
+
 .vitem &$tod_bsdinbox$&
 .vindex "&$tod_bsdinbox$&"
 The time of day and the date, in the format required for BSD-style mailbox
@@ -14333,16 +14351,12 @@ harm. This option overrides the &%pipe_as_creator%& option of the &(pipe)&
 transport driver.
 
 
-.option openssl_options main "string list" +dont_insert_empty_fragments
+.option openssl_options main "string list" unset
 .cindex "OpenSSL "compatibility options"
 This option allows an administrator to adjust the SSL options applied
 by OpenSSL to connections.  It is given as a space-separated list of items,
-each one to be +added or -subtracted from the current value.  The default
-value is one option which happens to have been set historically.  You can
-remove all options with:
-.code
-openssl_options = -all
-.endd
+each one to be +added or -subtracted from the current value.
+
 This option is only available if Exim is built against OpenSSL.  The values
 available for this option vary according to the age of your OpenSSL install.
 The &"all"& value controls a subset of flags which are available, typically
@@ -14354,12 +14368,19 @@ names lose the leading &"SSL_OP_"& and are lower-cased.
 Note that adjusting the options can have severe impact upon the security of
 SSL as used by Exim.  It is possible to disable safety checks and shoot
 yourself in the foot in various unpleasant ways.  This option should not be
-adjusted lightly.  An unrecognised item will be detected at by invoking Exim
-with the &%-bV%& flag.
+adjusted lightly.  An unrecognised item will be detected at startup, by
+invoking Exim with the &%-bV%& flag.
+
+.new
+Historical note: prior to release 4.78, Exim defaulted this value to
+"+dont_insert_empty_fragments", which may still be needed for compatibility
+with some clients, but which lowers security by increasing exposure to
+some now infamous attacks.
+.wen
 
 An example:
 .code
-openssl_options = -all +microsoft_big_sslv3_buffer
+openssl_options = -all +microsoft_big_sslv3_buffer +dont_insert_empty_fragments
 .endd
 
 Possible options may include: