Hello!
Thanks for writing back.
The short answer is that the post_id is available in the listing export. If you export the listings, you will have both the post_id and the email in one place. You would also have the address and category information, and so could conceivably even rebuild the permalink from the listing export CSV.
On the side of customization, I had several thoughts, but they are only ideas about how to proceed on your own or with a developer because it is outside what we can do here in support.
First, if you don’t want to go through the process of regularly merging that post_id information into your external database, you should look at making sure that the post_id is captured into your system, as the permalink does not have some intrinsic relationship to the post_id.
Second, if you wanted to use the listing owner’s wp account email, then you would need to look into running a SQL query or making an API connection.
You make a good point that we will keep in mind as we consider future email features for future versions.
Let me know if I missed something in your question, or if you want to ask it another way that might help us find a different solution.