Slow Mail.app in Lion OS X 10.7

I recently helped a client with a terribly crippled Mail.app on their Mac. They had upgraded to 10.7 (Lion) from 10.6 (Snow Leopard) not long ago and are a heavy user of Mail.app. Unfortunately, as seamless as upgrading OS X often is, installing a new system over an existing one sometimes brings current issues along with, or create new ones.

They reported that Mail.app would get so slow that typing would be delayed to an unusable extent.

Here’s the initial course of action I suggested:

  1. Install any updates by going to “Software Update” in the Apple Menu
  2. Open “Disk Utility” (find in Spotlight menu or in Applications folder > Utilities)
    1. Select your harddrive on the left pane
    2. Click “Verify Disk”
    3. Note if there are any errors reported once the process is done
    4. Click “Repair Disk Permissions” (errors are probably not important with this step)

This last step, “Repair Disk Permissions” is a sort of cure-all for Mac problems. It isn’t a specific, targeted, remedy, but often can solve problems (especially after something like a system upgrade.) In the case at hand, this was enough to fix the poor performance in Mail.app.

If this hadn’t solved the problem, I would have continued with the following, proceeding down the list if the problem wasn’t remedied:

  1. Remove all Mail preferences
  2. Remove all Mail files in the user Libary (this will remove all locally stored emails! Procede with caution and back-up!)
  3. Create a new user account and manually migrate your data

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