[Mailmunge] Add Header based on condition in filter_recipient{}

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I am hoping for a creative solution. I want to be able to add a header based on a condition that happens in the filter_recipient{}.

One idea explored was adding an identifier to a DB in filter_recipient{} and checking for it in filter_message{}.
However this is on postfix and the docs warn qid isn't reliable in filter_recipient{}.

I don't think tracking To: and Env-From: in a DB to identify it's the same email between filters is reliable.

I started to get excited when i saw privdata(), but it's not carried over between the two filters.

Any ideas how to accomplish this?