Hi,
According to the official document: Alert policies in the security and compliance center
We can know that 'Suspicious email sending patterns detected' is one of the Default alert policies.
Microsoft provides built-in alert policies that help identify Exchange admin permissions abuse, malware activity, potential external and internal threats, and information governance risks. On the Alert policies page, the names of these built-in policies
are in bold and the policy type is defined as System. These policies are turned on by default. You can turn off these policies (or back on again), set up a list of recipients to send email notifications to, and set a daily notification limit. The other settings
for these policies can't be edited.
In addition, you may also refer to the article introduces about How
to set up a multifunction device or application to send email using Microsoft 365 or Office 365 to make sure you correctly set the function.
This Microsoft Online: Exchange Online Forum will be migrating to a new home on
Microsoft Q&A, please refer to this sticky
post for more details.
Regards,
Joyce Shen
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