E-mail not received despite success message

Hello,

I have an issue with my client’s website : E-mails are not received, despite having the success/green border message. I tried changing the sender email, the recipient e-mail, i tried adding a new form.

E-mails are correctly sent and received with MailPoet, mailboxes works well (including the host’s one), flamingo works well.

Any idea?

Thanks

The page I need help with: [log in to see the link]