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51 lines
1.3 KiB
Markdown
51 lines
1.3 KiB
Markdown
Some email services like Gmail, Protonmail, etc don't have a strict SPF record (`-all`) to support the "classic" email forwarding
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that is usually used for group mailing list. In this scenario, an email is sent to a group is forwarded as-is,
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breaking therefore the SPF.
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A malicious hacker could use this security fail to impersonate your alias via the reverse-alias. This rarely happens
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as the reverse-alias is generated randomly and is unique for each sender.
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However if you want to prevent this kind of attack, you can enforce the SPF policy even if your mailbox uses a "soft" policy.
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1) Install `postfix-pcre`
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```bash
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apt install -y postfix-pcre
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```
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2) Add `/etc/postfix/body_checks.pcre` file with the following content
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```
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/^X-SimpleLogin-Client-IP:/ IGNORE
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```
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3) Add `/etc/postfix/client_headers.pcre` with the following content
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```
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/^([0-9a-f:.]+)$/ prepend X-SimpleLogin-Client-IP: $1
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```
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4) Add the following lines to your Postfix config file at `/etc/postfix/main.cf`
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```
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body_checks = pcre:/etc/postfix/body_checks.pcre
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smtpd_client_restrictions = pcre:/etc/postfix/client_headers.pcre
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```
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5) Enable `ENFORCE_SPF` in your SimpleLogin config file
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```
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ENFORCE_SPF=true
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```
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6) Restart Postfix
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```bash
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systemctl restart postfix
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```
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7) Restart SimpleLogin mail handler
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```bash
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sudo docker restart sl-email
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```
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