How to delete all emails at once in Gmail
This feature works on the Gmail web platform (not yet supported on the Gmail mobile apps), and the implementation is completely uncomplicated.
(Note: Deleting all emails doesn't mean deleting your entire Gmail account. You can still send and receive email after you've cleaned up all your existing emails.)
Delete all Gmail emails at once
First, open any web browser on your Windows, Mac, Linux, or Chromebook computer, and go to the Gmail website. Sign in to your Gmail account as usual.
On the Gmail interface that appears, in the menu bar on the left, click 'All Mail'. If you don't see this option, click 'More' to show more options.
On the corresponding screen that appears on the right, you'll see a list of all your Gmail emails, including archived ones. To delete all of these emails, you'll have to first select them all by clicking the 'Select' option at the top of the Gmail interface, as shown in the illustration below.
Immediately all emails displayed here will be selected. To select emails that are not on this page, at the top of the email list click the 'Select All X Conversations in All Mail' button, where 'X' is the number. volume of emails in the 'All Mail' folder.
All your emails are now selected. To start deleting them, at the top of the Gmail interface, click the 'Delete' option (the trash can icon).
You will see a confirmation message pop up. Click 'OK'.
Gmail will immediately begin the deletion process and move your emails to the trash folder, where they will continue to be stored for about 30 days before disappearing completely. If you want to delete them right away, the next thing to do is empty the trash. First, in the menu bar on the left side of the screen, click 'Trash'.
On the corresponding screen that appears on the right, click 'Empty Trash Now'.
In the 'Confirm Deleting Messages' message that opens, click 'OK'.
All your emails (except emails in the 'Spam' folder) are now deleted.
To delete spam emails, in the menu bar on the left side of the screen, click on the 'Spam' item. Then in the right pane click 'Delete All Spam Messages Now'.
Hope you are succesful.