Hello, I’m trying to find information on how the Mail app is storing the cache. Is it a true copy of the IMAP provider? Could you restore an IMAP server’s copy from the cache?
Essentially I’m trying to determine if the Mail cache is enough of a backup for an IMAP server if I choose the trust the cache enough, over having to setup a full backup IMAP server for mirroring.
The purpose of a cache is usually to store a limited set of data/information in a buffer to speed-up access of an application. It’s purpose is NOT to store a complete set of data nor to hold it as a data backup. I personally wouldn’t recommend to rely on an app cache as a backup solution - that’s an absolutely bad idea.
I’m more thinking of how the local Outlook client can create a local cache of the IMAP server which is a downloaded copy. While not a true backup, essentially the data is retained and can be restored or copied to a new location. I’ve used that method to transfer e-mail between servers previously. I totally understand the risks.
cache is usually to store a limited set of data
This is exactly what I’m trying to verify. Sometimes it’s limited, sometimes it’s an entire copy.
I think it doesn’t really matter if it is an entire copy or not, more important is the purpose of the data store and which rules apply to manage it. So better look for a solution which is under your personal control and where the main purpose is to keep a backup at a save place 
Except it does. I appreciate your effort unfortunately you’re not addressing the question but focusing on my intended use case. How I intend to use the product is entirely irrelevant to the question of how the caching functions.