@Oliver Häusler , Thanks for the follow-up and sharing additional info.
Regarding the error codes. Sending emails is async operation, and the 202 means that your request has been accepted and you can get the delivery result by either log diagnostic or event grid, however, when the email is added to the suppression list, typically, you will start to receive the email drop error if all the recipients in the suppression list and email is dropped.
For the logs to return values, you need ensure that you have enabled the Log Diagnostic and make sure it's being saved into Log Analytics workspace
Navigate to the ACS resource:
- Go to "Diagnostic settings" blade
- Select "+ Add diagnostic settings"
- Ensure that you selected email logs
and that the destination is set to Log Analytics
After enabling the above setting', the email logs will be saved and can be found under the Log Analytics or Logs blade under the ACS resource, and you should be able to see the suppression reason (SmtpStatusCode and EnhancedSmtpStatusCode). It may take a while for the logs to appear.
Just to highlight. Need to wait for the cool down period until that particular email being removed from the suppression list automatically which can take up to 2 weeks depending on how many times one tried to send emails to that alias.
Managed suppression list | lifecycle of email addresses that are suppressed
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