Can't Sync Mail between 2012 Mac Mini (10.15.7 Catalina) and IPhone 8( Version:16.7.2)??

If the accounts are IMAP it should sync automatically.

We need to see what all is running, a report from this will not display any personal info...

https://discussions.apple.com/docs/DOC-6172

EtreCheck is a FREE simple little diagnostic tool to display the important details of your system configuration and allow you to copy that information to the Clipboard. It is meant to be used with Apple Support Communities to help people help you with your Mac. It will not display any personal info.

https://www.etrecheck.com/

Thanks for Old Toad’s etrecheck instructions…

Slow iMac 2017 - Apple Community

Use the Note tool on the bottom of this editor's toolbar, as shown in the image, to copy and paste the output from EtreCheck. In a Reply before you click post, look for this to add longer texts...

You need to uninstall it or remove more than just the WD App...

/Library/LaunchDaemons/WDDiscoveryService.HelperTool.plist

Executable: /Library/PrivilegedHelperTools/WDDiscoveryService.HelperTool

WD Discovery/WD Discovery.app

/Library/Application Support/WDDesktop.app/Contents/Resources/kdd

Running app: /Library/Application Support/WDDesktop.app/Contents/Resources/wdsync

Running app: /Library/Application Support/WDDesktop.app/Contents/PlugIns/WDDesktopFinderSync.appex/Contents/

Or get App Cleaner & Uninstaller, which is my goto cleanup app…

https://nektony.com/mac-cleaner-pro

Or Mac Cleaner Pro...

https://nektony.com/mac-cleaner-pro

Delete these files & restart...

~/Library/LaunchAgents/com.adobe.ARM.***.plist

~/Library/LaunchAgents/com.amazon.music.plist

~ tilde indicates your home folder

Apple hid the Users' Library folders...

Method 1:

1 From the Finder, select the Go menu at top of the screen, and choose Go to Folder.

2 In the window that opens, enter ~/Library, and click Go.

Why are you running the WD software? It is generally a problem.

Safe Boot, (holding Shift key down at startup), does the problem occur in Safe Mode? Could take 10 minutes.

Safe mode attempts to repair Disks & clears lots of caches & loads safe Drivers, & prevents loading of 3rd party extensions, so if Safe Mode works try again in regular boot.

Manually Rebuilding Spotlight via Terminal

If the aforementioned Spotlight control panel approach doesn’t spur a reindexation of the drive, you may need to initiate it manually through the command line. Open Terminal and use the following command string to do so:

sudo mdutil -E /

This basically asks for temporary super user status, which is why Terminal may ask you for your password (it may not if you’ve used a sudo command recently or are already logged in as a super user or root. The command asks the unix tool mdutil to reindex the spotlight database for everything on the computer, including external drives, mounted disk images, etc. To re-index only for a specific drive, use the /Volumes path. For example, for an external drive named “MiniMe,” the command would look like this:

sudo mdutil -i on /

Rebuilding a drive index can take a long time, so be prepared to wait whether you do it through the System Preference panel or the command line.

If still need be…

Open Terminal and run each of these one at a time

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user

sudo /System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -seed -lint -r -f -v -dump -domain local -domain system -domain user -domain network

killall Dock

sudo mdutil -E /

sudo mdutil -i on /

Rebuilding a drive index can take a long time, so be prepared to wait whether you do it through the System Preference panel or the command line.

It should not interfere with Mail, except searching in Mail for a short time. :)

If the Drive is Formatted NTFS you may need the WD software to wrte to it, but if it's Formatted ExFAT, HFS+, or APFS then I'd uninstall the WD software.