Email notes

Bouncing unwanted spam

Edit Postfix configuration

Open /etc/postfix/main.cf with your favourite editor:

sudo nano /etc/postfix/main.cf

Find the line beginning with:

smtpd_recipient_restrictions =

If it doesn’t exist, you can add one near the end of the file. Add this rule near the top of that list (before other entries)

check_sender_access hash:/etc/postfix/sender_access,

It should look something like:

smtpd_recipient_restrictions =
    check_sender_access hash:/etc/postfix/sender_access,
    permit_sasl_authenticated,
    permit_mynetworks,
    reject_unauth_destination

2. Create the sender access map

Create or edit the file

sudo /etc/postfix/sender_access

Add an entry for the sender you want to reject. Example:

spam@example.com    550 5.1.1 User not known here

You can also block entire domains if you prefer:

example.com         550 5.1.1 User not known here

3. Build the lookup database

Run:

sudo postmap /etc/postfix/sender_access

This creates the corresponding

/etc/postfix/sender_access.db

4. Reload Postfix

Apply the changes:

sudo systemctl reload postfix

5. Test it

From an external email account, try sending a message from that blocked address.

You should see in your Postfix logs

/var/log/mail.log

something like:

NOQUEUE: reject: RCPT from mail.example.com[1.2.3.4]: 550 5.1.1 User not known here; from=<spam@example.com>

The sending server receives a permanent bounce (5xx), so it stops trying.