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 email@example.com on behalf of the user. Approving firstname.lastname@example.org as an authorized sender and/or whitelisting all email from the IP address 188.8.131.52 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.