Permanently Blocking Junk Emails

In Outlook for Windows, the normal Block Sender feature does not actually prevent the sender's message from reaching your mailbox. It simply tells Outlook to move messages from that sender to the Junk Email folder. There is no client-side Outlook setting that can make a blocked sender completely unable to deliver mail to your Exchange Online mailbox.

If this is a Microsoft 365 work or school account, the better solution is to block the sender at the Exchange Online/Microsoft 365 level. An administrator can add specific addresses or domains to the tenant's anti-spam blocked-senders list. Messages identified there are rejected or treated as spam before they reach the user's mailbox, depending on the configuration, so they do not accumulate in your Junk folder.

If you are dealing with hundreds of different garbage senders, blocking individual addresses is usually not the best approach because spammers constantly change addresses. Instead, use Exchange Online/Defender anti-spam policies, mail-flow rules, or sender/domain blocking based on the characteristics of the unwanted messages. Microsoft 365 administrators can also configure stricter spam filtering so these messages are handled before they reach individual mailboxes.

If this is a personal Outlook.com account rather than a Microsoft 365 organizational account, Outlook.com does not provide a true "reject this sender before delivery" option either. Blocking a sender primarily causes those messages to be filtered as junk. You can create rules and use Microsoft's filtering, but you cannot configure Outlook for Windows itself to refuse SMTP delivery from a particular sender.

To create a rule that automatically deletes messages from specific senders rather than letting them sit in Junk, in Outlook go to Settings > Mail > Rules > Add new rule. Give the rule a name such as "Delete garbage senders." Under Condition, select "From" and enter the sender's email address. Under Action, select "Delete." Save the rule. Messages from that sender will then be moved to Deleted Items rather than accumulating in Junk.

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hth

Marcin