Mailings -> New mailing gives 404 Not found (NGINX)
You have an error with the configuration of your nginx that doesn't properly redirect to drupal /civicrm/a/ but does it for /civicrm/a.

What configuration did you choose for your drupal/nginx? 
I started with that one and whitelisted a few more urls (in extern/ folder)
https://github.com/perusio/drupal-with-nginx and it works fine