How to Speed Up and Optimize Mac Mail

The good news is that you don’t have to switch email clients to handle your overloaded inbox, instead you just need to help Mail to get ‘back on its feet’ by forcing the app to rebuild the mailbox and to reindex all email messages. The process is quite simple, but it takes a bit of a time – depending on how big your mailbox is.

The first step, however, is to clean the junk/spam mail folders, which helps the software in its recovery process since no time is wasted on unnecessary garbage. It’s a good idea to automate the cleaning of junk emails by using a simple setting to delete them when it’s a month (or even earlier) old. This gives you enough time to review the junk email folder and save any email that isn’t spam.

How to rebuild a Mail inbox in three steps

Rebuilding a mailbox to update the list of messages it contains is a very simple process:

1. Launch Mail (if you haven’t yet done so).
2. Select a mailbox in the Mail left sidebar.
3. Click Mailbox > Rebuild.

When you hit Rebuild for IMAP or Exchange email accounts, all messages and attachments stored on your Mac are removed and then downloaded again from the mail server to your computer. Your mailbox will appear to be empty until the process finishes, which can take minutes or hours depending on how large your inbox is. Tip: don’t rebuild your inbox if you are on limited cellular data.

If you have multiple email accounts, you will need to repeat these steps for each of them.

How to reindex all messages in Mail app

An alert prompting you to fix the mailbox is a sign of a bigger issue, so addressing it immediately is the right choice to make. The good thing about it is that it can be done manually, and this particular process will also get the good old Mail app experience as good as new. This includes proper search results, as well.

Just follow the steps below:

1. Quit the Mail app and launch Finder.
2. Press Command + Shift + Go, and copy and paste the following path into the Go to Folder prompt: ~/Library/Mail/V4/MailData/
   1. Use “V3” if you are running macOS 10.11 El Capitan or “V2” for Mac OS X 10.7 through to 10.10. On macOS 10.6, the path is /Users//Library/Mail/Envelope Index.
3. In the MailData folder, select the files that begin with “Envelope Index” and move them to Trash.
   1. Tip: You could move them to the Desktop or Downloads as a backup in case something goes wrong.
4. Close the MailData window and relaunch Mail.

Doing this will force Mail to reindex all messages, so this will take a while depending on the size of the mailbox. Rebuilding the mail index database is completely safe.

After rebuilding your mailbox and forcing the software to create a new index database, all the attachments you have sent and received will be downloaded again to your Mac. That has the potential to wipe out gigabytes of storage space on your startup disk. Also, it is worth considering that Mail – like every other application that runs on your computer – builds up a cache, which could get corrupted and cause Mail to act strangely again.

Mac optimization apps such as CleanMyMac, MacKeeper, CCleaner, and the like (we have reviewed the majority of them) will help you keep the Mail app and the whole computer in a good shape by removing cache files from time to time. Also, these apps can help you save disk space by removing the downloaded Mail attachments, which are stored on the Mail server and can always be redownloaded on demand. It’s better that the attachment doesn’t occupy space on your Mac until you need it.