Blocking a Sender

Part of the Security Fundamentals section of Coddy's Cybersecurity journey. Lesson 32 of 43.

Quarantine removes a message that has already arrived. But what if the same sender keeps sending more? A sender block tells Lumen to reject new messages from that domain.

For example, if fake payment notices keep coming from lumen-help.test, block that domain:

seclab mailblock lumen-help.test

You should see:

Blocked mail from lumen-help.test. New emails from it are rejected at the gateway.

Messages that arrived before the block are still in the inbox, so you must quarantine those separately. Check the spelling before blocking a domain so you do not stop mail from a real supplier.

If you block the wrong domain, you can allow its emails again with:

seclab mailunblock lumen-help.test

You should see:

Mail from lumen-help.test is delivered again.

Use mailblock for email domains. The block command you learned earlier is for connections from IP addresses.

Challenge

Easy

Ticket from Omar, finance

The same fake sender keeps sending overdue-payment messages. Find and block its domain so new copies cannot arrive. Quarantine the copy already here and mark it as phishing. Keep real supplier mail and Lumen's internal mail arriving.

Try it yourself

Terminal

Blocking a Sender

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