I've recently switched our servers from Apache to NGINX. While testing our WP Form Builder Add-on, I found that my web server took pretty long time for the mail function to process, however, on the local server, everything works pretty smooth.
While digging Google, I found the solution which fixed this issue. If you are facing the same problem, follow the steps below to resolve it.
Log in to your server via SSH as root user and run the following command:
You will find an entry which looks like this
All you need to do is add localhost.localdomain after this so it should look like this:
127.0.0.1 localhost localhost.localdomain
Press CTRL+X and then Y to save the file. Now, your server mail should process in nanoseconds.
Sometimes, a small fix with a few characters here and there can waste hours. I thought I'd share this here so that it will save some of your time.