Knowledge Base

Emails sent from external mail services are rejected by DMARC checker on a Plesk server: REJECT message for [email protected]

Symptoms

The option Enable DMARC to check incoming mail is enabled in Plesk at Tools & Settings > Mail Server Settings.

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:

Connect to the server via SSH.
Create a backup of the original /etc/postfix/main.cf file:

# cp /etc/postfix/main.cf /etc/postfix/main.cf_orig
Open the /etc/postfix/main.cf in a text editor. In this example, we are using the vi editor:

# vi /etc/postfix/main.cf
Change the smtpd_milters value as follows:
```
smtpd_milters = , inet:127.0.0.1:12768
```
If the non_smtpd_milters option exists, make its value empty:
```
non_smtpd_milters =
```
Save the changes and close the file.
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