Updating Contact Details through Excel

Recently I came across a problem where I realized that all of the e-mail addresses within my system were incorrect. The default email addresses that come with the demo environment are @contoso.com, and my demo tenant has the domain name of @contosoeastfoxtrot.onmicrosoft.com.

I wanted to change them all so that when I try to skype any of the other employees in the demo system, that all of them would work. I could have been minimalistic and just change one of the users, but if you are going t...