Boy I've tried.
I've removed individual email accounts (i.e. Gmail and Outlook).
Then attempted to see if corporate email (i.e. Exchange/O365) is doing things to drain battery - especially since we have hard rules about max history of one month and found that the Mail app cleans out overnight....
But there's something weird in the Mail app. Can't figure it out.
Good info about the corporate email and the rules.
I would recommend that you log a support-case with your IT dept. There are LOADS of settings and tweaks that can be done from the management software side and there are new settings constantly added to keep up with the devices.
Sometimes these settings create issues and talking from experience its only when users start reporting issues its being looked at. Not sure what your company recommends but Outlook is a better option than Apples mail app if you guys are using Exchange/MS365.
If they enforce using Outlook as the "corporate" mail-client they could prob get rid of the policy settings for the standard mail app and possibly solve the issues you are experience.