i got sent this mail this morning, i use thunderbird and it downloads all my mail to me, i assume it then deletes the mail from the server

i went to the webmail box and theres nothing in there, so im wondering whats up

The mailbox site-help@domain.com is almost full. You should remove some emails from the box as soon
as possible to prevent losing any future mail. This mailbox is currently 91.92% full.