Hi Josh Davidson,
I agree that the Additional email recipients should also receive the alerts.
I have often seen the alerts get blocked before for people who had spam filters on their emails, so they should make sure to check their spam and junk sections. If possible, the receivers should also make sure that they allow the sender of azure-noreply@microsoft.com
. If the users have any email security products, or if you have any conflicting email application rules, the alerts may also get blocked.
If you have already checked for all of those variables, another consideration is whether the right severity level of the incident for those recipients. You can also do a detection test from the page where you download the onboarding package script at security.microsoft.com to confirm.
[https://learn.microsoft.com/en-us/microsoft-365/security/defender-endpoint/configure-email-notifications?view=o365-worldwide#troubleshoot-email-notifications-for-alerts
Let me know if this helps. If the users still face this issue I'll be happy to troubleshoot over email.
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