Added openssl_verify_mode parameter for action_mailer.

- parameter in `environments/production.rb`
- documentation & default value (nil) in `discourse_defaults.conf`

config/discourse_defaults.conf

@@ -63,6 +63,10 @@ smtp_authentication = plain
 # enable TLS encryption for smtp connections
 smtp_enable_start_tls = true
 
+# mode for verifying smtp server certificates
+# to disable, set to 'none'
+smtp_openssl_verify_mode =
+
 # enable MiniProfiler for administrators
 enable_mini_profiler = true