Why Does the Apple Mail App Use So Much Storage on iPhone?
You barely use Apple Mail, or only read plain text messages — yet when you open your storage settings, Mail sits near the top, eating 5GB, 10GB, or more. If you are wondering why Mail takes up so much space on your iPhone, the short answer is cached attachments, and the fix takes about two minutes.
Why does Mail take up so much space on iPhone? Mail bloats your storage because it caches attachments. Every PDF, high-resolution photo, signature image, or video clip that lands in your inbox is downloaded as a local copy so you can view it. Over years, those downloaded files pile up into a large hidden cache. The email text is trivial in size — the attachments are the weight.
Here is exactly how that cache forms and the safe way to clear it without losing a single email.
Cached Attachments and Email Signatures
If you think you rarely get big attachments, you are probably forgetting signatures.
Many companies embed high-resolution logos, promo banners, or animated GIFs in their email signatures. Each time you open a message from that sender, Mail downloads those images into its cache. Add the occasional 50MB work PDF or a relative sending video by email instead of iMessage, and the Mail cache grows steadily. Because it is buried in the app's system data, there is no in-app "Clear Cache" button to wipe it.
Why Mass-Deleting Emails Doesn't Work
Your first instinct may be to delete thousands of old messages. It is mostly wasted effort.
The text of an email takes near-zero space. You could delete 10,000 promos, empty the Mail trash, and recover only a few megabytes. Deleting a message also does not reliably purge the large attachment it carried from the hidden cache. You need a more direct approach.
| Where the space goes | Realistic impact |
|---|---|
| Email body text | Negligible (megabytes total) |
| Signature logos & banners | Small individually, large in aggregate |
| Document & media attachments | The main cause — often several GB |
| Deleting messages | Frees little; doesn't reliably clear the cache |
| Re-adding the account | Clears the whole cache at once |
How Do I Clear the Mail Cache on iPhone?
Because Apple gives Mail no "Clear Cache" button, the most effective method is to make iOS dump the cache by removing the email account and re-adding it.
Is this safe? Yes. Your emails live on a cloud server (Google, Microsoft, Yahoo, iCloud). Deleting the account from your iPhone only severs the local link and clears the local cache — it does not delete your address or any messages. Sign back in and your inbox reappears within moments; anything you open again simply re-downloads from the server on demand, so you never lose access to an attachment you still need.
How to do it:
- Go to Settings > Mail > Accounts.
- Tap the account causing the problem (for example, Gmail or Outlook).
- Tap Delete Account at the bottom. If you have several accounts, repeat for each.
- Restart your iPhone so iOS fully flushes the deleted cache from active memory.
- Return to Settings > Mail > Accounts, tap Add Account, and sign back in.
Check Settings > General > iPhone Storage > Mail again and the app should be back to a few hundred megabytes. Before you start, confirm you know each account's password and two-factor method so signing back in is painless.
Keeping the Mail Cache From Growing Back
A few habits slow the rebuild:
- Turn off "Load Remote Images" in Settings > Mail to stop signature graphics and tracking pixels from downloading automatically.
- Limit offline mail by reducing how much each account syncs, if your provider's settings allow it.
- Save important attachments to Files and delete the email, rather than letting Mail keep a permanent cached copy.
- Unsubscribe from heavy newsletters that send large image-rich emails daily, since each one caches its graphics.
These steps won't make Mail's cache zero — that is normal and expected — but they keep it from quietly returning to several gigabytes.
How Is This Different From Mail on a Mac?
On a Mac, Apple Mail stores entire mailboxes and all attachments locally by default, which is why Mail can occupy tens of gigabytes there. On iPhone the cache is leaner and managed more aggressively by iOS, so the re-add-account trick is usually all you need.
The principle is the same on both: the message text is tiny, the attachments are the weight. If you manage attachments at the source — saving the ones you need and letting the rest stay on the server — Mail stays small on every device. There is no way to keep an iPhone's Mail cache permanently empty while using the app, and you shouldn't try; a small working cache is what makes the app fast.
Frequently Asked Questions
Will deleting my Mail account delete my emails? No. It removes only the local copy and cache on your iPhone. Every message stays on your provider's servers and re-downloads when you sign back in.
Why doesn't Apple give Mail a "Clear Cache" button? iOS manages app caches automatically in the background, but Mail's attachment cache is treated as part of the account's local data. Removing and re-adding the account is Apple's de facto reset.
How often should I do this? Only when iPhone Storage shows Mail using several gigabytes you cannot explain. For most people that is once or twice a year, not a routine task.
Still Out of Space? If you cleared Mail but the "Storage Full" warning keeps returning, the real weight is almost certainly in your camera roll.
Stop manually curating photos. Use a dedicated media utility like Clenoir to automate it: Clenoir isolates your heaviest 4K videos so you can delete the biggest files first, and groups blurry, duplicate burst shots for fast, safe review. Everything removed goes to Recently Deleted for 30 days, so you can clear gigabytes in minutes with no risk — see more in our free up iPhone space guide.