Plesk for Linux
kb: technical
Symptoms
- SPF, DKIM and DMARC are enabled
-
smtpd_sender_restrictions
in/etc/postfix/main.cf
already includereject_sender_login_mismatch
- The following error is visible in
/var/log/maillog:
CONFIG_TEXT: Jan 31 12:06:49 server postfix/smtpd[17653]: 1F52940A96: client=spoofed.example.org[203.0.113.2]
Jan 31 12:06:49 server psa-pc-remote[22555]: 1F52940A96: from=<> to=<mail@example.com>
Jan 31 12:06:49 server postfix/cleanup[30887]: 1F52940A96: message-id=<20230131120524.8E710E5016B@spoofed.example.org>
Cause
The Postfix security measures are not strict enough and the mail server can still be abused.
Resolution
Install the Plesk Email Security extension and follow these steps:
1. Log into Plesk
2. Go to Tools & Settings > Plesk Email Security > Server Settings > Advanced
3. Under the Postfix - Strict Rules section, check the Enable strict rules box
4. Click Save
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