Knowledge Base

Unable to receive external Email on a Plesk hosted mailbox: from unknown[2001:db8:f61:a1ff:0:0:0:80]: 5.7.23 SPF validation failed

Symptoms

Email cannot be delivered to [email protected]. The following entries are found in /var/log/maillog.

postfix/smtpd[1485479]: connect from unknown[2001:db8:f61:a1ff:0:0:0:80]
postfix/smtpd[1485479]: ADAE01BA122D: client=unknown[2001:db8:f61:a1ff:0:0:0:80]
psa-pc-remote[2888394]: ADAE01BA122D: [email protected] [email protected]
...
psa-pc-remote[2888394]: ADAE01BA122D: spf: stderr: DATA REPLY:550:5.7.23 SPF validation failed. : Reason: mechanism
psa-pc-remote[2888394]: ADAE01BA122D: spf: stderr: REJECT
postfix/cleanup[1485551]: ADAE01BA122D: milter-reject: END-OF-MESSAGE from unknown[2001:db8:f61:a1ff:0:0:0:80]: 5.7.23 SPF validation failed. : Reason: mechanism; [email protected] [email protected] proto=ESMTP helo=<mail.example.net>
SPF spam protection to check incoming mail is enabled under Plesk > Tools & Settings > Mail Settings with fail/deny SPF checking mode.

Cause

Sender SPF record does not contain 2001:db8:f61:a1ff:0:0:0:80 as permitted sender.

Resolution

Sender should adjust the DNS SPF record to allow the IPv6 address from the maillog error or change the IP address from which outgoing emails are sent to match the one from the current SPF record.