Hi Tim,
It is not something we have had to do previously, so I can just share my opinion/speculation on what I think should work.
I would love it for you to try out and let me know how you get on.
From a technical point of view -
In the Marketing App, when we send a marketing email, we can specify the From email address. If you set this to be the email address of a mailbox you have previously set up, when the customer replies to your marketing email, it should get tracked.
From best practise point of view -
I don't really like it. I would not recommend it!
The problem is (even if it worked) that you start mixing up normal emails and marketing emails.
Just out of interest, what is the scenario and what is your marketing email about? Usually you would send a customer to a marketing page, events, newsletter, etc, rather than ask them questions and expect them to reply.
Better practise would be in your marketing email to give them an alternative email address to reply to if they wanted to get in touch and give them a code to quote if you needed to track/link that back to your campaign / customer journey.
Thanks,
-DD