Have you tried adding a custom field to the criteria? If you scroll to the bottom of the criteria list where subject and from as located is customize.

You can add any header field to the customize dialog. I have a whole list of field in mine for managing list-id, reply-to, even message id. Once it is added it appears in the list of action just as any of the default entries. The big caveat is that the filter acts on the first instance of the header it sees, so for things like "received:" which can have many occurrences the results are very patchy.

I kinda figured that would be the answer, but I am not sure how to do it. Should the custom field be "deliveredto:" and the text should be "[email protected]"? No, that doesn't seem to work. I set the custom field to "deliveredto" (the colon is not accepted) and it doesn't seem to filter when I choose "Run now".

I d not use identities much, but how you set up things in Gmail might actually have an impact.

I suggest you select a mail that meets your criteria, open it and press CTrl+U to see the source and have a look at the headers. You might find the To: contains the original address and you can filter on that. Or it might be something like apparently-to: or there may be x- headers added by Gmail that will identify the oringinal account.

There is a list of header in appendix A of the document linked, including links to the RFC's where they are defined https://datatracker.ietf.org/doc/html/rfc2076#appendix-A

Thanks! The custom field that worked for me was X-Forwarded-For

According to what I see in the headers, there are probably a few other fields that would work just as well.