If you delete any Gmail message, it is automatically stored in the trash folder. For delete message permanently you need to go trash folder and select particular or multiple emails to remove from trash folder.
• First, you need to open Gmail.
• On the left side of Gmail, click on more and then click on Trash folder.
• Open the particular message and click on delete forever.
• For deleting all messages in your trash folder you need to click on empty trash now option.
So follow each step as given above and fix this error by yourself. For more help, you can browse Gmail support helpline.