Mail function before redirect to Paypal

Hi,

There is no reason for that. The email sent after the order is created and the email sent after the order payment is validated uses the exact same function.

The only thing I could see is that your email server could reject the email because the email encoding is not correct, or because it uses HTML and not the other one, etc.

You could try to switch the settings in the mail configuration of HikaShop like the encoding on the "add name" option, the multipart option, etc.
Also, you should ask your hosting company why such thing could happen and send them your HikaShop email settings. They know better than us we their email server could reject an email.

One thing is sure, is that it doesn't come from HikaShop since it works on all other websites

Do you mean in emails ? You could try changing the encoding in the configuration.

Could you try to add the code

<INPUT TYPE="hidden" name="charset" value="utf-8">

Yes. That sounds like a nice improvement