Color coordinated email identification (internal vs external email addresses)
When you are drafting a new email or replying to an existing email - have the email addresses of the to/cc participants be a different color, which identifies quickly the recipients that are internal vs external. This could be done by identifying in outlook the @microsoft.com vs @abc.com email addresses and color accordingly.
Why is this helpful? For larger companies sometimes you don't know the 30 people on an email. When you need to take an email thread internal - you have to click on each email to remove the external participants.
If they were color coordinated - you would quickly be able to see that you removed all external participants... or that there were no 'external' emails and you can send the internal items. :)