Mail automatically being deleted on MacBook Air, after install of CleanMyMac X.

Part 1 of 2

Ditto to @ BobTheFisherman

To add and this may seem harsh .

Any Third Party Applications that will interfere with the normal operation of the OS,  is an invitation for disaster and comprising the Operating System

Certain Applications maybe available on the Apple Apps Store - this only means the Developer is prepared to pay Apple a portion on each sale. What the Application may do to the computer is up to the User to check this out before purchase

Any of the below should be removed as per Developers Instructions

1 - Disk Cleaner 

This will include CleanMyMac , aka “ BrickMyMac “

Read some of the posting and arrive at your own conclusions.

Part 2 of 2 

Specific to CleanMyMac aka “ BrickMyMac “

The steps in #1 below is predicated on the Offending  Application has been Removed as per the Developers Specific Instruction 

#1 - Some Contributors suggest restarting in Recovery Mode and choosing to Reinstall the Operating System over  the existing installation. 

This may or may not replace elements of the Entire Operating System including the Home Folder ( User Account )  and replace any corrupted or removed elements of the Operating System and make thing right.

#2 - Then there are Other Contributors ( like myself ) would suggest  from this link Use Disk Utility to erase a Mac with Apple silicon.

For Intel computer >> Use Disk Utility to erase an Intel-based Mac followed by How to reinstall macOS

Thereafter to start from scratch and install all Required Application directly from the Apple Apps Store or Directly from the Developer.

If going this route - I suggest Not using Startup Assist to migrate things back as this will probably Re-Introduce the existing  issue that existed when the TM Backup was made 

Firstly and more importantly >>

You are welcome 👍 and thank you too 😀

Do come back to the Apple Support Communities ( ASC )  in the future, if / or when additional questions may arise

Part 2 of 2 🤞 and hope the below helps

1 - Due diligence before downloading and installing any Application including Applications from the Apple Apps Store.

This may keep from getting " Clutter " on the machine that later has to removed

If that Clutter needs to be removed, some Developers offer Specific Instructions to remove their Application while other do not

2 - Prudence on what is downloaded and Really Needed in the long term versus a One Off need

3 - Generally, the Operating System is very well equipped to manage the Operating System on its own without Third Party interventions.

After all, who knows the innards of macOS better than Apple ( we, including myself sometimes think differently - humour here )

4 - IMHO, if Apple felt it was paramount to have Disk Cleaning Application, the would have it Built into the Operating System. Yes Microsoft Windows does have some but that is Windows

5 - System cache files do but up over time and can be easily remove but frequently Shutdown and Restarts

6 - To hasten the System cache clearing process - Restart in Safe Mode. This will perform a Disk Repair, clear cache files and only load Apple Software, extensions and fonts. The boot up will be slow and can take some time - Normal.

I know this seems humorous, but according to MacPaw, the cleanest way to uninstall CleanMyMac, is to use CleanMyMac uninstaller. It will get rid of all its companion files along with the .app file.

I agree with the other posters here that it is far more problematic to have CleanMyMac than it offers in terms of value. It gets in the way of many functions. Also, if you have Anti-Virus or other 3rd party utilities that claim to make macOS better, get rid of those too.

First priority, uninstall CleanMyMac and reboot.