Hi All - Some info on this. I have done some digging on the Microsoft side and have a current case open. Some e-mails to an Outlook (my domain is @hotmail.com) account that mentions Finance, or Banking, or Mortgage in the subject header are automatically ignored by Microsoft. They do not even make it to the account in question that will have a ‘Safe Senders’ list with monzobank.com approved on there.
This is an ongoing challenge with older Hotmail-based domain names, and Microsoft are struggling to make it work. Interestingly - it works with my work e-mail address that is Office 365. I would highly recommend that Magic Link e-mails be sent to an e-mail address that is NOT a Hotmail domain but to any others where you have complete control of the mailbox.
Monzo employees - this may be something you can take up with Microsoft directly, because I have had my first house purchase massively impacted by not being able to receive e-mails from Monzo, my Lawyer or my Estate Agent.