This is just completely frustrating, my business requires sending email to my clients sometimes it takes more that 15 minutes to arrive and sometimes it does not arrive at all!, which is completely unacceptable, what makes it worse is that i found out that you don't allow the use of external smtp services because i'm looking into using gsuite as my email provider. Why would you not optimize your email services if you don't want people to use external services?. just completely unacceptable specially now that i'm stuck and forced into using a very slow email service.
I'm sorry to hear you're having email issues. Are you using an email client or are you accessing your email through Webmail? Feel free to provide additional details so others in the community can share suggestions.
You can also use G Suite as your email provider, you will just need to configure your MX records to point to their services. If you decide to use their email services you can change your domain's MX records by following the steps in this guide.
I'm using PHPMailer library and I already had all my mx records set and verified by google, in fact my code has passed when i tested it on my local machine, it sent out email via google's relay server as expected, but your server keeps spitting out "SMTP ERROR: Failed to connect to server: Connection Refused(111)" but works fine when i try to use the relay server that you provided, but as i said, I wanted to use google's service because its faster and more reliable.