Apple Mail can silently consume 20-100 GB of a Mac's internal drive. Unlike a webmail client, it downloads real copies of your inbox to disk.

Short answer: the bloat is almost always downloaded attachments and signature images. Change the Download Attachments setting, then either wait for macOS to reclaim the space or re-add the account to force a clean slate.

Why Mail grows so much

By default, Mail downloads every attachment it sees. A few years on a corporate account — with heavy PDFs, slide decks, and logo-laden signatures — and the local cache is enormous.

Those attachments live deep inside ~/Library/Mail, hidden from normal Finder views.

The safe fix: change Download Attachments

  1. open Mail and click Mail > Settings in the menu bar
  2. open the Accounts tab
  3. select your account
  4. under Account Information, change Download Attachments from All to None or Recent

This stops new attachment downloads. Existing ones shrink over time as macOS reclaims them, especially with Optimize Mac Storage enabled in the Apple ID settings.

The fast fix: re-add the account

Because mail actually lives on the server, removing the account from your Mac only deletes the local cache.

  1. open Mail > Settings > Accounts
  2. select the bloated account
  3. click the minus (-) button to remove it
  4. wait for the local data to clear
  5. click plus (+) and add the account back
  6. before the sync starts, set Download Attachments to None

Nothing is lost on the server side.

Better next routes

If Mail is clean but the drive is still full, continue with How to Find Large Hidden Files on Mac.

For the broader cleanup framing, use What Is Purgeable Storage on Mac?.