Mail Storage
Also known as: Mail app storage, email storage iPhone, mail attachments cache
Mail Storage is the space the iOS Mail app uses for messages and, mainly, the attachments it downloads to view them offline. Most of it is a cache: deleted attachments simply re-download from the mail server when you reopen the message.
- Mostly cached, downloaded attachments
- Attachments re-download from the server
- No universal in-app cache button on iOS
Attachments are the bulk
When you open an email with photos, PDFs, or other files, Mail downloads them so they display instantly and remain available offline. Over time these cached attachments accumulate and become the largest part of Mail’s footprint in Settings > General > iPhone Storage > Mail.
The messages themselves are usually small; it is the saved attachments that drive the size, especially across busy or long-standing accounts.
How to reclaim the space
Because attachments live on the mail server too, clearing the local cache is low-risk: the file re-downloads the next time you open that message. iOS offers no single "clear cache" button for Mail, so the common resets are to remove and re-add the email account, or to delete and reinstall the Mail app, which clears the downloaded attachment cache.