I have the problem here that I have a forwarding in my activity log for a mail address that I have not set up and certainly does not belong to my domain. The recipient address belongs to the domain @web.de ^^. This is very strange.
Is it possible that the mail was addressed to someone @web.de^^ but also sent to an address that belongs to you, possibly as a BCC?
I have seen this for emails I get from mailing lists, where my address is not in the To: header of the messge. Frequently the To: header contains the list address, and thats what Cloudflare reports in the activity log, even though that address is not in my domain. The mail gets delivered to me via my address in the SMTP envelope, but Cloudflare doesn’t report that.
after using the mail routing for a few days now, your hint seems to me to be the explanation. At first it is a bit disturbing to see such a forwarding in the activity log.