7bit Mail Encoding breaks DKIM on Plesk Postfix

[websavers]

Hey friends,

Just a heads up that using 7bit (and possibly 8bit) SMTP message encoding in the WHMCS General Settings (Mail tab) *will* cause DKIM headers to break if you're using Plesk Postfix. It's possible this occurs with other Postfix implementations as well.

Messages sent via WHMCS to services like outlook.com/Hotmail/Live Mail (and probablty many others) will probably be filtered to spam as they detect a DKIM signature mismatch, resulting in a fail report.

The simple solution was to change the encoding to base64 in the WHMCS settings. Test messages sent from WHMCS to Outlook.com addresses and Hotmail addresses then resulted in a DKIM pass.

Hope this helps others trying to figure out if/why their DKIM isn't working properly.

-Jordan @ websavers.ca

[WHMCS Lawrence]

On 4/18/2019 at 10:11 AM, websavers said:

Hey friends,

Just a heads up that using 7bit (and possibly 8bit) SMTP message encoding in the WHMCS General Settings (Mail tab) *will* cause DKIM headers to break if you're using Plesk Postfix. It's possible this occurs with other Postfix implementations as well.

Messages sent via WHMCS to services like outlook.com/Hotmail/Live Mail (and probablty many others) will probably be filtered to spam as they detect a DKIM signature mismatch, resulting in a fail report.

The simple solution was to change the encoding to base64 in the WHMCS settings. Test messages sent from WHMCS to Outlook.com addresses and Hotmail addresses then resulted in a DKIM pass.

Hope this helps others trying to figure out if/why their DKIM isn't working properly.

-Jordan @ websavers.ca

Thanks for the informative post! This appears to be a mail server-specific issue as it has been observed with Zoho and others as well: https://help.zoho.com/portal/community/topic/zoho-break-dkim-signatures-body-hash-if-8bit-encoding-are-used-through-smtp

Basically anytime 7bit encoding is used, it can break DKIM.

[websavers]

1 hour ago, WHMCS Lawrence said:

Thanks for the informative post! This appears to be a mail server-specific issue as it has been observed with Zoho and others as well: https://help.zoho.com/portal/community/topic/zoho-break-dkim-signatures-body-hash-if-8bit-encoding-are-used-through-smtp

Basically anytime 7bit encoding is used, it can break DKIM.

Good to know! It might be worth considering removing the 7-bit and 8-bit encoding options from WHMCS, after all deliverability of the messages sent through WHMCS is quite important.

-Jordan