Trying to sendemail to multiple recipients (worked with GMail account, not with Office365)

I had a program sending emails to multiple people fred@xxx,sally@xxx and this worked for years using my company google mail account. We switched to office365 and now it only sends to a single person (seemingly the last person in the list). Apparently "," is not the delimiter for Office365. Can't seem to find info on how to string together emails for Office365.