SMTP services start rejecting mails sent by WHMCS after a few hours

[Flaunt7]

I have tried SMTP services like G SUITE, Zoho Mail, Mailgun. 

All of them work fine for 12 hours and after that they start to reject sending mails. and then I have to switch to php mail which sends the mail to spam. 

I called the Zoho mail support team and they too couldn't identify the issue. 

Zoho mail had been working completely fine for 2 years but from the last 1-2 months this issue persists. 

We have not sent even a single marketing/spam email yet. 

The domain name is flaunt7.com 

I did not create a ticket with WHMCS directly before regarding this as their support sucks. The (IDIOT) support representatives ask to point out every thing so that they can identify the issue. They are never able to solve even simple issues. I seriously ask the WHMCS support team to improve their service. Their support just SUCKS! 

[steven99]

What is the rejection / bounce back that you get back? 

[Flaunt7]

With G Suite, I get a message error SMTP data not accepted. 

 

And also, I created a ticket with WHMCS and this time too they did not take an in depth look and just said it is issue of SMTP provider. 

But how can it be issue of SMTP provider when it is suddenly happening with dozens of SMTP providers. And when it had been working perfectly for 2 years. 

 

[steven99]

For at least gsuite, contact their support and see if they can provide more info.  Only thing I can think of right off is a spam filter is blocking for some reason.