RE: How to check if emails are actually sent?
Try this:
We have noticed that e-mails came if the sender is the default account (surveys@email.formspro.microsoft.com), but not from our (first) customized sender's email.
The important thing is this: we have several customized senders e-mails. All of them, which were created by adding them manually in the admin interface worked.
However, the one, we added some time ago with the help of Microsoft did not work. Microsoft recently added the option to add customized sender's e-mails by ourselves.
Action: Delete the customized sender e-mail, added before this update and re-enter it (manually). It worked for us.