Exchange Online redirect rule doesn't reset "To" address

My configuration goal is to forward / redirect a message going to a mailbox to an external site (its an email capture setup).

I was using forwarding, which is straight forward but includes the original "To" address in the recipients, and the email capture thinks its part of the group. Reply-alls to the messages it sends doubles and then triples the number of active cases.

Then I found that "Redirect" seems to be a keyword that does EXACTLY what I want - it forwards the mail as if it was sent directly from the sender, without notifying the sender nor the "redirecting" email box. Except its not doing that. If I can get this to work as advertised, that's all I need.

My second attempt was to modify the headers - Remove "To" and then redirect the message, which adds the "redirect" address as the recipient, and has no idea there was a forwarding address. It worked.. Except if there is more than one address specified by the To header. It removes all of the addresses specified in To. But customers can frequently add coworkers or other parties, and the email capture does "reply" to all recipients, which is what we want. Just not the original forwarding / redirecting email.

So is there a way to

1. Get "Redirect" to work as advertised
2. Only Remove part of a header, perhaps via a substitute regex
3. Replace or delete a single recipient.
4. Some other cool and nifty way to forward without taking along the forwarding / redirecting address.

Thanks in advance.

If it is possible to allow the email to be sent to original recipients, you can create an Exchange mail flow rule and use Bcc as an action to add the external site as an additional recipient.

The rule may look like: