Symptoms
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The option Enable DMARC to check incoming mail is enabled in Plesk at Tools & Settings > Mail Server Settings.
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Emails sent from external mail services are rejected by DMARC checker, because SPF/DKIM record (or both) was not found. The following entries appear in
/var/log/maillog:dmarc[16748]: Starting the dmarc filter...
dmarc[16748]: SPF record was not found in Authentication-Results:
dmarc[16748]: DKIM record was not found in Authentication-Results:
dmarc[16748]: DMARC: REJECT message for [email protected]
postfix-local[16746]: message discarded by a mail handler
Cause
The Postfix before-queue mail filter is either not defined:
# grep smtpd_milters /etc/postfix/main.cf
smtpd_milters =
or disabled:
# grep smtpd_milters /etc/postfix/main.cf
#smtpd_milters = , inet:127.0.0.1:12768
As a result, SPF/DKIM checks are not performed and the email is rejected by DMARC policy of the sender.
Resolution
Configure the Postfix before-queue mail filter:
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Connect to the server via SSH.
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Create a backup of the original /etc/postfix/main.cf file:
# cp /etc/postfix/main.cf /etc/postfix/main.cf_orig
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Open the /etc/postfix/main.cf in a text editor. In this example, we are using the vi editor:
# vi /etc/postfix/main.cf
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Change the
smtpd_miltersvalue as follows:smtpd_milters = , inet:127.0.0.1:12768
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If the
non_smtpd_miltersoption exists, make its value empty:non_smtpd_milters =
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Save the changes and close the file.
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Verify the changes:
# grep -ir milt /etc/postfix/main.cf
smtpd_milters = , inet:127.0.0.1:12768
non_smtpd_milters = -
Restart the Postfix service to apply the changes:
# service postfix restart
with