Office 365 - Nag to use BCC if certain conditions are met during email composition?

[pete]

My ideal is something like this:

 

• Person begins writing an email with more than 10* external** recipients in the "To:" field
  
• OWA shows a tooltip bar across the top of the composition window with "Check if you should be using BCC" in a non-annoying way. Similar to the configurable mail tips.
  
• Person adjusts to BCC if necessary
  

 

*or another number unlikely to trigger false positives

**not a domain registered to the Office 365 tenancy.

 

....but I'm not convinced it's doable in the OWA client.