Email trail with my own Domian

I want to do a trail run with 365  only using a couple of (my domain) emails and leave the rest of the office using the old  POP Server?

Is this possible, as  Step 4 says I must add all e-mails, and the old service will no longer work.   How can I get around this to see if 365 will work in my office enviroment.

Cheers

Jay