a prelimiary IPv6 support, HTTP listen

src/mail/ngx_mail_core_module.c

diff --git a/src/mail/ngx_mail_core_module.c b/src/mail/ngx_mail_core_module.c
index 10e6c8b..a9cd6a4 100644
--- a/src/mail/ngx_mail_core_module.c
+++ b/src/mail/ngx_mail_core_module.c
@@ -305,6 +305,11 @@
         return NGX_CONF_ERROR;
     }
 
+    if (u.family != AF_INET) {
+        ngx_conf_log_error(NGX_LOG_EMERG, cf, 0, "listen supports IPv4 only");
+        return NGX_CONF_ERROR;
+    }
+
     cmcf = ngx_mail_conf_get_module_main_conf(cf, ngx_mail_core_module);
 
     imls = cmcf->listen.elts;