How to delete all mail in iCloud

"How to delete all mail in iCloud: I want to delete all mail stored in iCloud. Howto?"

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Deleting All Files on iCloud:

Why so? If you need this for further keeping, then I highly-recommend exporting all of your mail, for archival and recovery purposes. Use a Mac for this, as it is required for creating an archives and backups. Elsewise, add it to a third-party app, on your iPhone.

As Apple Warns Here:

WARNING: Deleting a mailbox permanently deletes the mailbox and its contents (including other mailboxes), and can’t be undone.

Frist...

I. Add your Apple iCloud Account:

1. Go here: Set up iCloud Mail on All your Devices - Apple Support
2. Scroll to: Set up iCloud Mail on your Mac
3. Proceed from there as necessary.

then...

II. Export the Mail, for Backup (If Desired):

For recovers purposes, creating a backup of all of your mailboxes is best. You can add this to an external hard drive, or store it on your Mac.

1. Go Here: Import or Export Mailboxes in Mail on Mac - Apple Support
2. Scroll to: Export mailboxes
3. Proceed from there as necessary.

then...

III. Perform the Deletion:

1. Go Here: Create or Delete Mailboxes in Mail on Mac - Apple Support
2. Scroll to: Delete mailboxes
3. Proceed from there as necessary