The Mail app uses iPhone storage by caching attachments and message content as you open emails. The reliable way to clear it is to remove and re-add the email account (which flushes the local cache while your mail stays on the server), since iOS gives Mail no direct "clear cache" button. Your emails are safe — they live on the mail server and re-sync.
TL;DR
- Mail's storage is mostly cached attachments and downloaded messages, not the emails themselves.
- iOS has no "clear Mail cache" button — the clean fix is remove + re-add the account.
- Your email is safe: it lives on the server (Gmail, iCloud, Outlook) and re-downloads.
- Check the size in Settings > General > iPhone Storage > Mail.
- Large attachments you opened are the main cache bulk.
Why does Mail use storage?
When you open an email with photos or a PDF, Mail downloads and caches it on the device so it opens instantly next time. Over months, those cached attachments and message bodies add up. The Mail app itself is small; the Documents & Data line is the cache. iOS does not expose a button to clear just that.
How to check Mail's size
Settings > General > iPhone Storage > Mail shows the split between App Size and Documents & Data. If Documents & Data is large, the steps below will reclaim it.
How to clear Mail storage safely
The dependable method is to remove the account and add it back — this flushes the local cache without touching anything on the server:
- Settings > Mail > Accounts.
- Tap the account (e.g. Gmail or iCloud).
- Tap Delete Account (or Sign Out).
- Re-add it via Settings > Mail > Accounts > Add Account.
Because IMAP/Exchange mail lives on the server, your inbox re-syncs and nothing is lost — only the local cache is rebuilt fresh and smaller.
You can also reduce future cache by limiting how much Mail syncs (some providers let you cap days of mail) and by deleting large emails with attachments you no longer need.
What iOS does natively, and where it stops
iOS keeps Mail's cache automatically and re-fetches on demand — for most people Mail is not a big drain. Where it stops: there is no per-app cache button for Mail, so the account refresh is the only reliable manual clear. And Mail is rarely the largest item; the storage list will usually point you elsewhere first.
Clear the bigger drains too
If Mail showed up on your storage list, large videos and duplicate photos are almost certainly bigger. Cleanor for iPhone finds those on-device in one pass. For the full routine, see the free up iPhone space guide.
What this cannot do
Removing the account clears only the local cache, not server-side mail, and a POP account (rare today) may keep mail only on the device — check before deleting. There is no way to clear Mail's cache without the account refresh on current iOS.
FAQ
How do I clear Mail cache on iPhone?
iOS has no Mail cache button. Remove the account (Settings > Mail > Accounts > [account] > Delete Account) and add it back — this flushes the local cache while your server mail re-syncs.
Will deleting my Mail account delete my emails?
No, for IMAP/Exchange accounts (Gmail, iCloud, Outlook) your mail lives on the server and re-downloads. Only legacy POP accounts may store mail locally.
Why is Mail using so much storage?
Mail caches the attachments and messages you open so they load instantly later. Years of cached attachments build up in the app's Documents & Data.
Is there a faster way than re-adding the account?
Not on current iOS — there is no direct cache clear for Mail. Limiting sync range and deleting large attachment emails helps slow the buildup.
Next: how to clear app cache on iPhone without deleting apps and iPhone storage full but nothing to delete. To clear the bigger media drains, get Cleanor for iPhone.