Emails not being received

I notice that most of the time, my contact form admin notifications are not received in my mailbox, while the notifications for the form submitter seem to come in without any issue.

I have installed a email logging, so I’m sure the emails are being sent out propperly. I also notice that both emails (for the admin as for the client who is filling in the form) the ‘from email address’ is the same: [email protected].

For testing, I just made 7 form submits. All seven are well received by ‘the client’ (sent to my private icloud email address), but only 3 are received by the admin. How is this possible? What can be the cause of that and how can I fix it?

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