I installed Office 2016 on my home computer. I use it with multiple Gmail and Yahoo accounts. The Yahoo account is my main default account.
I have also set up an Exchange account so my wife can get her work email.

Since setting up Exchange, I was able to change the Yahoo account to be the default for emailing from. I noticed though that the default data file is the exchange file. It won’t let me change it to Yahoo.

1) Does it matter what the default data file is?
2) What is the default data file actually used for? (as I assume the different data files are associated with their own email accounts)