This mail cannot be forwarded because it was detected as spam

Mail
1

Why do I now keep receiving this message when I email known and previously-messaged recipients?:

This mail cannot be forwarded because it was detected as spam

Has the recipient received the email? Has it even been sent? Who is spamming? What is the fix?

2

Without seeing the error, it is difficult to say where it comes from, but probably that message comes from your email provider. You might want to ask them why they consider it as spam.