There is no way to delete all your emails in bulk using BT webmail.
If you want to delete multiple emails try the following
If you hold down the shift key then tick the box to the left of the first email you want to delete in the list of emails then scroll down using the scroll bar on the right hand side or use the PgDown key and tick the last email you want to delete then release the shift key. It will select all the emails in between. You can then click delete or drag and drop them into the Trash folder.
When selecting the emails keep the number less than 150 at a time.
You can also tick the box in the menu bar above the boxes you have been ticking and that will select all the viisible emails in your list.
