Request Release of quarantined email to be sent to external user

Question

I work for a 3rd party IT company that manages a handful of Microsoft 365 tenancies for our clients. We are looking to move away from our current spam provider and use Microsoft's services instead.

Over the past week or so, I have been been testing Microsoft Defender policies, quarantine notifications and more to see if this is a viable solution for us. The only part I am getting stuck on is the following: When users request the release of an email (due to the high severity, they cannot release it themselves), I want this to email our external IT Support email address to notify us of the request. This address is located on a different domain and different tenancy.

I've added the email address as a Guest User in Azure which gives me the option to select it as a recipient for the 'User requested to release a quarantined message' alert, but I dont seem to ever receive it!

My thoughts have been to have this go to an internal account (in the tenancy the quarantined message is located), and have a rule to forward this externally, or try find a way with Power Automate (even if its just forwarding the email) - but these solutions just seem messy and surely there must be a better option.

Any other IT techs out there experienced this/have a good solution?