diff --git a/cookbooks/exim/templates/default/exim4.conf.erb b/cookbooks/exim/templates/default/exim4.conf.erb
index ffc8be609..3558af884 100644
--- a/cookbooks/exim/templates/default/exim4.conf.erb
+++ b/cookbooks/exim/templates/default/exim4.conf.erb
@@ -753,6 +753,9 @@ signed_smtp:
   multi_domain = false
   hosts_try_dane =
   tls_require_ciphers = <%= node[:ssl][:gnutls_ciphers] %>:%LATEST_RECORD_VERSION
+<% if node[:exim][:external_interface] -%>
+  interface = <%= node[:exim][:external_interface] %>
+<% end -%>
 
 
 # This transport is used for handling pipe deliveries generated by alias or
diff --git a/roles/fafnir.rb b/roles/fafnir.rb
index bb6b7b667..d3bfcc115 100644
--- a/roles/fafnir.rb
+++ b/roles/fafnir.rb
@@ -7,6 +7,7 @@
     :last_address => "10.0.79.254"
   },
   :exim => {
+    :external_interface => "<;${if <{${randint:100}}{90} {184.104.226.98;2001:470:1:b3b::2}{87.252.214.98;2001:4d78:fe03:1c::2}}",
     :routes => {
       :openstreetmap => {
         :comment => "openstreetmap.org",