fix Auth-Method, the bug has been introduced in r2496
diff --git a/src/mail/ngx_mail_auth_http_module.c b/src/mail/ngx_mail_auth_http_module.c
index ec1dcdc..d66b5ee 100644
--- a/src/mail/ngx_mail_auth_http_module.c
+++ b/src/mail/ngx_mail_auth_http_module.c
@@ -139,6 +139,7 @@
 static ngx_str_t   ngx_mail_auth_http_method[] = {
     ngx_string("plain"),
     ngx_string("plain"),
+    ngx_string("plain"),
     ngx_string("apop"),
     ngx_string("cram-md5"),
     ngx_string("none")