Messages to outlook.com fail DKIM check but no other company fails it

Question

I'm trying to send emails to people that have outlook.com or have their domains email hosted by office 365 from my business email server and I keep going to SPAM. In the headers it looks like maybe the reason is a DKIM failure. But, DKIM passes for all other companies I've sent emails to (Google, Yahoo, comcast, etc.).

Web searches show others having this issue but the resolution is unclear. Outlook.com doesn't seem to care or want to respond.

I'm at a loss right now on what to do. Anyone able to help or have suggestions?

Answer 1

I thought I had found out what the problem was, at least for my emails. I use a From header in the form: pi.sebi.org <*** Email address is removed for privacy ***>

No other email provide would change this header in transit, especially since it is DKIM signed. However, it seems that Microsoft’s devs thought they could just add double quotes to the From header while relaying my email, changing it to: “pi.sebi.org” <*** Email address is removed for privacy ***>

I also suspect that certain email fields are being changed prior to the DKIM calculation and are invalidating the DKIM check. When I compare email headers across different platforms, the one outlier is outlook. Here are the h fields in my DKIM-Signature: h=Content-Transfer-Encoding: Content-Type: Message-Id: Date: Reply-To: From: From: Subject: Subject: Mime-Version: List-Id: To: To: List-Unsubscribe: List-Unsubscribe-Post: Sender.

When I compare AOL, Gmail, Yahoo, and Outlook, I get the same headers across AOL, Gmail, and Yahoo (which match up to original message that I sent). Outlook differs in these fields.

Field	AOL, Gmail, Yahoo Values	Outlook Value
Content-Type	text/html; charset="utf-8"	text/html
Date	Mon, 02 Dec 2024 22:12:02 GMT	Mon, 2 Dec 2024 22:12:02 +0000
Reply-To	Name <******@domain.com>	"Name" <******@epicpass.com>
From	Name <******@domain.com>	"Name" <******@domain.com>

My "To" field was already quoted, but I suspect that outlook would quote that value as well.

To be fair, I am getting my header values through a 3rd party tool so I suppose it's possible that some intermediary server is making these modifications. It's hard to tell when an email is passed server-to-server in a pipeline. If anyone has more information about this, it would be helpful.