I've only gotten one interview invite thus far, and it was delivered to the email that I included on my application. I don't think schools/PIs will expect us to use/check anything other than the email address we asked to be reached at!
I found mine by looking at a university's "Career/Jobs Website." Just google desired university with "career/jobs," and you should find a webpage with a list of open RA positions that you can apply for.
If the person who posted that they received an interview invite from Ohio University just so happens to see this - Would you mind sharing the POI's initials? Thank you.