MacOS High Sierra 10.13.6 - Mail App - Setting Custom Retention Intervals for mailboxes

I'm trying to edit the default email retention values provided in the Mail App. I'm reviewing the plist files for Mail, but I cannot find which plist file contains the default email retention values.


I found the below link as a reference:


https://www.macworld.com/article/1140865/keepmail.html


This article states they are located in com.apple.mail.plist, but this article is outdated and these values are no longer stored in this file 😟


I'm using MacOS High Sierra 10.13.6.


Does anyone have any advice on how I could locate the correct file? Does anyone know where the correct file is exactly located?


Thanks for the help!