The Apple Mail program can cause several problems as the result of high CPU use such as overheating. This document offers some suggestions for resolving these issues.

Tools for Monitoring

It’s generally a good idea to use the Activity Monitor to track what programs seem to be excessive in their CPU utilization. The Activity Monitor is found in the Utilities folder, which is in the Applications folder. In addition to viewing the CPU tab in the main display, you can also click on CPU Usage found in the Window menu. This allows you to see the overall use of your CPU cores (and virtual cores) at a glance.

Another helpful tool is the TG Pro (Temperature Gauge Pro) software that reports on the many temperature monitors in Apple computers. High temperature can result in your computer CPU slowing down, called throttling. So, keeping the computer cool can help it run faster.

Problem Identification

You can start and use a program, like Apple Mail, to identify and isolate problems using the above mentioned tools. If when you launch Apple Mail, the CPU utilization goes high and stays high, that could indicate an underlying issue.

Reducing Excessive CPU Utilization

Here are some suggestions for reducing excessive CPU utilization by the Apple Mail program.

  1. ACCOUNTS. It is common to have several email accounts and checking them from one program like Apple Mail can be very convenient. If you use Apple Mail to check dozens of email accounts, it could result in excessive CPU usage. Consider having only your essential accounts configured to be checked by Apple Mail. If necessary, you could use another email client such as Thunderbird or Outlook to periodically check email accounts that aren’t your primary accounts.
  2. DRAFTS. When emails are created but not sent, they are typically retained as drafts. These can be saved on your device, or saved on the email service provider system. If you are having an internet connectivity problem, or for some other reason unable to store on the cloud server, your draft may be lost. Saving drafts on your local device is usually faster and more reliable. However, if you store drafts on your device, they won’t be available on other devices to continue working on — such as starting an email on your smartphone and then continuing it on your desktop computer. Some people continually have dozens of uncompleted emails and move from one device to another. For such people, saving locally could be inconvenient. However, for most people, saving to the local device won’t present a problem.
  3. EMAIL RULES. An excellent tool for saving time is to use Email Rules. If you use many different email rules, then your computer will be burdened with intensive processing of all your emails. Try to use a dozen or fewer rules if possible, establishing rules that achieve the greatest benefit in reducing the messages you need to manually process. If possible, have rules isolated to specific email accounts so the rule isn’t running on all email accounts.
  4. FOLDERS. Periodically review the folders you have for organizing emails. Try to reduce the number of folders as much as possible to reduce the complexity of the file system. Don’t inconvenience yourself by having fewer folders than you need, but simply have what you need and nothing more.
  5. INDEXING. Emails are indexed to provide faster results when searching. The indexing process catalogs all email content and keywords. If you have many emails saved this can take a while. Reducing emails saved online can help.
  6. SAVED EMAILS. Over time, emails accumulate on email systems. If you’ve allowed thousands of emails to accumulate over many years, then your computer is synchronizing and indexing all those thousands of emails. Slow email service response times can result in unexpected issues. Because Apple Mail lacks a detailed display of activity, you may not know specifically what tasks are being processed. You can move emails to local folders under the “On My Mac” header in Apple Mail. This removes the emails from the servers. You can create folders and subfolders to recreate the inbox and sent items of your different accounts. A security benefit is that if an account were to get hacked, the hacker does not have many thousands of private emails spanning several years. Also, if you are a regular user of the Apple Time Machine backup software, you can ensure your emails are backed up safely. Emails saved locally will be easier to manage because there are no delays interacting with service providers.
  7. SMART MAILBOXES. The Apple Mail program lets you save searches as Smart Mailboxes. So, you perform a search, save it by clicking the small save button below the search box, and then the search results will be available as a Smart Mailbox that is continually updated with the latest results. You can right click on a Smart Mailbox to enter more detailed search specifications for the Smart Mailbox. This makes Smart Mailboxes very helpful because you can perform a search within defined search criteria, such as “search for all emails from a specific person” and then “among those emails search for messages that contain a specific word.” Having many complicated Smart Mailboxes can place a burden on your computer because it will be continually trying to index and display the emails that meet the search criteria. Delete Smart Mailboxes when you no longer need them, and use them sparingly. If you can use them as a short-term tool, that will help.
  8. THUNDERBIRD. A email program called Thunderbird from Mozilla (the browser people) has some advanced features and more reliable operation than Apple Mail. It can be very useful for diagnostics because it provides more detailed information about the tasks being processed. Thunderbird is also useful if you have many email accounts to check. You could sue Thunderbird to check some, and use Apple Mail to check others.

Additional Considerations

Here are some additional performance considerations.

  1. BROWSER TABS. Web pages can have excessive ads, animations, and videos, that continue running even when you are not watching the page. These can be as processor intensive as other programs. It’s best to close out all tabs that aren’t absolutely necessary. Whenever possible, close all tabs and exit your browser. On Apple computers, you may see a notification about excessive battery use or processor utilization by Chrome or another browser.
  2. CLEAN RESTART. When shutting down or restarting an Apple computer it is possible to choose to have the computer started with the same programs, documents, and browser tabs open that were present at the time the system was shut down. There is a checkbox next to the option “Reopen windows when logging back in.” It’s better to remove the checkmark for that option and instead manually shut down all programs, save files, and close all browser tabs. This will help the computer have a cleaner simpler startup.
  3. LOGIN ITEMS. Some programs are configured to automatically start ever time the computer is turned on. It’s better to only run programs when they are needed. Go to the Apple Menu (top left of screen) and choose System Preferences > Users & Groups > Login Items and review the list of programs. Remove any unnecessary items by selecting them and clicking the minus symbol.
  4. PROGRAMS. When you are done with a program, close it out. Too many programs running can cause excessive CPU utilization.


Using the CPU and temperature monitoring tools suggested above can help you diagnose performance issues while making the above improvements. This will help you see if you are making progress.