imac mail is slow to download

Hello canoeak,

Thanks for that info and for choosing the Apple Support Communities. If we understand correctly, you are having an issue with the Mail app on your Mac loading slower than you expect. To help with this, please follow these steps from this Apple resource for this situation If your Mac runs slowly - Apple Support:

"Your computer’s startup disk may not have enough free disk space. To make disk space available, you can move files to another disk or an external storage device, then delete files you no longer need on the startup disk. macOS can also help you optimize storage by storing files in the cloud and helping you identify files you no longer need. Choose Apple menu  > System Settings, then click General in the sidebar (you may need to scroll down). Click Storage on the right, then click the storage recommendations you want to use. 

An app you’re using may require more memory than your Mac has easily available. You can use Activity Monitor to see how much memory your Mac and apps are using. See View memory usage in Activity Monitor. Also see the documentation that came with the app to find out its system requirements.

Quit any app that isn’t compatible with your Mac. For example, an app may require a different processor or graphics card. See the documentation that came with the app for information about its system requirements.

To see what processor your computer has, choose Apple menu  > System Settings, click General  in the sidebar, then click About on the right.

To see which graphics card your computer has, choose Apple menu  > System Settings, then click General  in the sidebar. Click About on the right, then click System Report. Click Graphics/Displays to see the name of the graphics card installed your computer.

Quit any apps you’re not using.

If you have problems with your disk, use Disk Utility to verify and try and fix any issues."

Next, to isolate this further, use safe mode to start up your Mac as it does the following things:

• Verifies your startup disk and attempts to repair directory issues, if needed
• Loads only required kernel extensions
• Prevents Startup Items and Login Items from opening automatically
• Disables user-installed fonts
• Deletes font caches, kernel cache, and other system cache files

Log in to your user account and test the issue while in safe mode and then restart normally and test the issue again.

How to use safe mode on your Mac - Apple Support

Cheers!