Allow exim access to dovecot auth-client.

states/email/dovecot_local.conf

@@ -18,3 +18,10 @@ protocol imap {
   mail_max_userip_connections = 40
 }
 
+# Allow client auth to exim4.
+service auth {
+    unix_listener auth-client {
+    mode = 0660
+    group = Debian-exim
+  }
+}