No confirmation email sent

Hi,

I just installed Ninja and it seems to work fine, however…

Every client should get a confirmation mail of what they’ve ordered.
But the don’t get the confirmation mail.

When I use the mail connected to my site, I do get a confirmation mail.
Using any other mail makes sure there’s no confirmation mail sent.

My website is https://www.peashasselt.be/bestellen (it’s in Dutch though…)