Registration Emails not leaving OJS to the wider world

Hi,

We are using OJS version OJS 3.3.0.19.
When a user registers, they get a screen that says a confirmation email will be sent to them, but the user never receives any email. It is not present in the SPAM folder or anywhere. The logs even don’t even show any record of the email being sent. We even asked our hosting provider to try to register.

All other emails are received.
We can even email the user directly from the OJS dashboard

We have checked that require_validation=0 and is not commented
We contacted our hosting provider to get the appropriate SMTP details

We have looked that RegistrationForm.inc.php file and the USER_VALIDATE email is being called.

From trawling through the OJS forum and the web, we note that the USER_REGISTER email was discontinued from version 3, but USER_VALIDATE is still active.

Would anyone be able to provide some advice on this please?