On occasion spam filters do block the emails sent from Intervals. Checking a spam filter is definitely the best place to start.
If that does not turn out to be the culprit, all emails from Intervals are sent from firstname.lastname@example.org on behalf of the user. Approving email@example.com as an authorized sender and/or whitelisting all email from 184.108.40.206 may do the trick as well.
If you have any questions or need help please contact our support team and let us know that you are having trouble receiving emails from Intervals.