My iMac has slowed when loading email and web pages. I

Download and run Etrecheck.  Copy and paste the results into your reply. Etrecheck is a diagnostic tool that was developed by one of the most respected users here in the ASC and recommended by Apple Support  to provide a snapshot of the system and help identify the more obvious culprits that can adversely affect a Mac's performance.

Copy the report

and use the Additional Text button to paste the report in your reply.

Then we can evaluate the report to see if we can determine the cause of the problem.

Hey there blufreezi,

The speed in which your emails load will depend on your Mac and network. You can try connecting to another network to help isolate the issue a bit further and test if it continues there.

Continue with the guidance below to help with your Mac running slow:

• 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.

If your Mac runs slowly - Apple Support

Take care!

You didn't follow the instructions I posted for copying and adding the report to your post. It's not in the Additional Text field - only the file path to the app in your Downloads folder. Read my previous post carefully and follow them explicitly.