Yes. This is best achieved by using Marketo custom objects.
You will have to create a custom object to hold all the RMA / Debit numbers for a lead (email address)
Then you will have to upload this data in to that custom object.
Once uploaded, confirm that data is uploaded correctly by going to one of the lead's information and checking that custom object.
Then in the actual email, you will have to use 'Velocity email scripting' to loop through the custom object and print out the information in a tabular format. There are some gotchas / peculiarities involved with this. Please feel free to reach out if you get stuck Rajesh@BrightAspects.com
Here are some useful links.
Thank you. That's a lot to learn up on in a week or so but I will see what I can do!