Why are my forwarded emails going to spam?

We sign everything, but in the end the receiving party decides which email go to spam.

When this happens for emails that go through KaiMail, there are two separate causes:

1. Authentication issues — If DKIM, SPF, or ARC is not correctly configured on the sender side, receiving servers will distrust the message. You can check if this is true from the ARC-Authentication-Results (AAR) of the email forwarded by KaiMail. You can also verify the authentication headers using Google Admin Toolbox or MXToolBox Header Analyzer
2. Content filtering — Even with correct authentication, messages with sparse content, suspicious links, or patterns that resemble spam can still be scored as junk by the receiving server. This is independent of authentication and outside KaiMail's control.

Verify that the authentication is clean first. If that checks out, the issue is in the message content itself or the original sender's domain reputation.