Why Apple Mail is using So Much Disk Space and How to Fix It?

admin | Apple Apple Mail how to | 4 minutes read | Modified on: 11-09-2026

If you ever got a dreaded message from your Mac saying, “Your startup disk is almost full,” it is most likely that Apple Mail is causing the problem. The problem with Apple Mail for some users is that it takes up tons of storage space—tens or even hundreds of gigabytes—without you being aware of it, causing poor performance and your Mac to be unable to install any software updates.

To understand how Apple Mail takes up so much storage space and what should be done about it, one must know how the app handles messages, caches, and attachments.

Why Does Apple Mail Take Up So Much Storage?

Apple Mail is meant to deliver the most streamlined and instant emailing experience. It is done by caching almost all data passed in your inbox. This, eventually, results in immense bloat of your Mac because of multiple reasons:

Heavy Attachments and Inline Images

Whenever you open any email that contains high-resolution pictures, PDF documents, presentations, and video clips, Apple Mail will automatically download them on your local drive. In case you are constantly working with large file emails, your ~/Library/Mail folder will grow immensely during a few months.

Caching and Offline Storage

Modern standards for email (IMAP, Exchange) allow mirroring the content of your mailbox directly on your machine, to enable searching and reading emails while being offline. Despite the fact that you have deleted some emails in your phone or browser, local indexes (Envelop Index), as well as caching and sync data, will still stay on your machine.

Several Accounts and Old Databases

Using several email accounts (freelance, personal, corporate) on one Apple Mail application makes things even worse. Additionally, if you used to have some email accounts but have stopped using them, their databases will stay in ~/Library/Mail and occupy lots of gigabytes.

How to Check Your Mail Storage Usage?

It is important to determine how many megabytes Apple Mail is taking up before any action is taken.

  1. Start by clicking on Apple Menu in the upper left-hand corner of your screen and choosing System Settings.
  2. Navigate to General > Storage (or About This Mac > Storage > Manage).
  3. Check the details of Mail storage and find out its actual gigabyte usage.

Manual Methods to Reduce Apple Mail Storage

You can reclaim disk space using several built-in macOS techniques, though they require patience and careful navigation.

Option A: Change Attachment Download Settings

Stop Apple Mail from automatically downloading attachments:

  1. Launch Apple Mail and then go to Mail > Settings (Preferences).
  2. Choose the Accounts tab and click on your email account.
  3. From the Account Information tab, look for Download Attachments.
  4. Make sure that you change the setting to None or Recent. This way, your attachments will remain stored on the mail server.

Option B: Clean Out Junk and Trash Folders

Deleted files may not be automatically deleted right away. Make sure that you empty your Trash and Junk folders on a regular basis:

  1. Apple Mail: Click on Mailbox > Erase Deleted Items and then select the account.
  2. Go to Mailbox > Erase Junk Mail for spam folders.

Option C: Rebuild Mailboxes

  1. If you feel like your mailbox space is inflated owing to corruption in the index file, rebuild your mailboxes to reduce their size:
  • Choose a mailbox from your side panel.
  • Go to Mailbox > Rebuild from the top menu.

How to Fix the Error using Strong and Effective Solution

Whereas manual cleaning and attachment control might help only for a while, they seldom present any solution to addressing the real issue of database bloat when you need to keep your historical emails for legal or professional purposes. In case you find that your Mail folder does not want to decrease in size, there is only one way out – keep all your historical data in an offline archive.

And here MacMister Apple Mail Converter comes into play.

How to Use MacMister’s Solution to Clean Up Your Mac?

Step 1. Download and install the app on your computer running on Mac OS.

Step 2. Open the software and then choose the Add File(s) and Add Folder(s) options to import the Apple Mail database (stored in ~/Library/Mail/).

Step 3. Choose the file format in which you want to convert the email (such as PDF for smaller document files or MBOX for saving raw files).

Step 4. Choose the location where you want to export the file, preferably on some external drive or online drive.

Step 5. Export the converted file. Now the files are ready for deletion, and you can free up a lot of disk space from your system.


Why to choose the App?

Created with a focus on handling large Apple Mail database archives, this professional tool enables you to export, compress, and convert your emails into compact, searchable formats (PDF, PST, MBOX) that you can easily transfer to an external hard drive or even cloud storage.

  • Free Up Gigabytes of Space Right Now: Export old client archives from your main startup volume to an external drive and drastically reduce the space taken up by the ~/Library/Mail folder.
  • Safeguard Your Data Intact: All email metadata, such as sender/recipient information, dates and times, hyperlinks, and attachments will be preserved without fail.
  • Choice of Output Format: Your Apple Mail data is convertible into PDF format (for record keeping), MBOX, PST, EML, and many others.
  • Safe Transfer of Folder Structure: Your carefully organized nested folders/subfolders structure will be transferred intact.

.Epilogue

An overcrowded database of Apple Mail could bring your Mac to its knees and lead to constant storage problems. Changing your attachment settings, cleaning up all junk files and using a professional service such as MacMister file conversion utility for transferring your history to an external hard drive would allow you to get rid of storage problems once and for all.