I'm having issues with my emails which Wordpress should send after my clients buy something on my website. 

They're not sent and I don't understand where it's exactly the problem, at the hosting company or Zoho mail?

So I have a domain fliostand.com and 2 email users there. They work fine with AirMail for example, so MX records and all is good. 

But when it comes to the Wordpress notifications nothing happens. I tried SMTP and other plugins for WP and nothing works. I've activated from my hosting also the ' Configure server to not accept mail locally and send mail to the lowest MX record.' and still nothing works. 

GoDaddy support says that a cause might be that I have two e-mail accounts on the same domain (for example max@fliostand.com and john@fliostand.com) and the server doesn't know where to send the e-mail. Is this a real issue or they just don't know what they talk about? Because outside Wordpress the e-mails work fine. 

What is the solution? Should I really delete one e-mail account?

Thank you and looking forward for a solution as the notifications are a crucial issue.

Vlad