My customers are not receiving an email sent from Pardot because they are being marked as spam.
I've checked the email using Litmus. Litmus shows that DKIM, SPF, DMARC are fine but flags that the List-Unsubscribe header is set as an URL rather than mailto. Litmus also shows that the Microsoft Exchange Online Protection Spam Score is 9.0 I understand that Outlook does not process URL based List-Unsubscribe and requires a mailto instead.
It appears that the Pardot List-Unsubscribe URL is causing the issue because when I send the same email HTML minus the unsubscribe link from Netsuite it passes the Microsoft spam check with a score of 1.0. The absence of a List-Unsubscribe is flagged by Litmus however it does not seem to have the same effect on the score.
In Pardot there doesn't appear to be any option to either change the "go.pardot...." unsubscribe link page or to add a mailto option.
Is it likely that the URL based List-Unsubscribe is what is causing the Pardot emails to fail Microsoft spam checks, and if so how do other senders successfully get emails delivered to Microsoft users?
I have never heard of the mailto option or the unsubscribe link causing issues with Microsoft spam score, but you can flip go.pardot to a secure vanity URL as explained here: https://www.pardot.com/blog/ssl-vanity-domains-now-available/. Hope it is helpful.