Hi,
Are you trying to add some email address which looks strange to the blocked sender list? If this is the case, I'm afraid currently it's the expected behavior in Outlook. Only normal SMTP addresses can be filtered by Outlook Junk Email filter.
As a workaround, we can create Outlook rules to move these email to Junk Email folder or permanently delete them.
In addition, I'd recommend you submit a feedback about this issue to Microsoft via the
UserVoice forum, which is the most direct channel our product team utilizes to collect suggestions and ideas from our customers. The product team will consider whether to change
the behavior according to customer needs.
Thank you for your understanding.
Regards,
Steve Fan
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