Forwarded to devs Outgoing DKIM not working with unauthenticated user

[DennisAm]

TITLE:

Outgoing DKIM not working with unauthenticated user​

PRODUCT, VERSION, OPERATING SYSTEM, ARCHITECTURE:

Plesk Obsidian 18.0.21 Update #4, ‪CentOS Linux 7.7.1908​

PROBLEM DESCRIPTION:

When sending emails through e.g. WordPress using unauthenticated SMTP (that is, not providing a username/password but just a From: ... address), the message is not signed with DKIM. Only when using authenticated SMTP (that is, by providing a username and password for sending email), DKIM works.​

STEPS TO REPRODUCE:

• Activate DKIM for domain using these instructions
• (specific to our situation, not sure if this is necessary to be able to reproduce the error) add DKIM public key to DNS
• Create a WordPress website on the domain, e.g. DOMAIN.TLD (though, any PHP script using the default PHP mail() function should reproduce this problem)
• Send an email through WordPress using [email protected] (by default, WP doesn't do any SMTP authentication and will attempt to use the default PHP mail() function)
• The receiving party will see in the email headers that the message is not signed with DKIM (see example headers below)

Then, try the following:

• Create email user in Plesk for DOMAIN.TLD, e.g. [email protected]
• Install WP Mail SMTP and use the following settings:
  • Server: localhost
  • Port: 25
  • SSL/TLS: none
  • User: [email protected]
  • Password <your password>
• Send an email through WordPress using [email protected]
• The receiving party will see in the email headers that the message is correctly signed with DKIM (see example headers below)

ACTUAL RESULT:

When sending from WordPress (unauthenticated, [email protected]):

Authentication-Results: spf=pass (sender IP is 149.*.*.*)
smtp.mailfrom=SENDER.nl; RECEIVER.nl; dkim=none (message not signed)
header.d=none;RECEIVER.nl; dmarc=pass action=none
header.from=SENDER.nl;compauth=pass reason=100

When sending from authenticated user ([email protected]):

Authentication-Results: spf=pass (sender IP is 149.*.*.*)
smtp.mailfrom=SENDER.nl; RECEIVER.nl; dkim=pass (signature was verified)
header.d=SENDER.nl;RECEIVER.nl; dmarc=pass action=none
header.from=SENDER.nl;compauth=pass reason=100

EXPECTED RESULT:

When sending from WordPress (unauthenticated, [email protected]):

Authentication-Results: spf=pass (sender IP is 149.*.*.*)
smtp.mailfrom=SENDER.nl; RECEIVER.nl; dkim=pass (signature was verified)
header.d=SENDER.nl;RECEIVER.nl; dmarc=pass action=none
header.from=SENDER.nl;compauth=pass reason=100

When sending from authenticated user ([email protected]):

Authentication-Results: spf=pass (sender IP is 149.*.*.*)
smtp.mailfrom=SENDER.nl; RECEIVER.nl; dkim=pass (signature was verified)
header.d=SENDER.nl;RECEIVER.nl; dmarc=pass action=none
header.from=SENDER.nl;compauth=pass reason=100

ANY ADDITIONAL INFORMATION:

​

YOUR EXPECTATIONS FROM PLESK SERVICE TEAM:

Confirm bug​

 

[IgorG]

Thank you for report. Bug was confirmed and submitted as PPPM-11366