how do i stop someone generating emails from my domain email address

[kindelephants]

Hi Help Anyone. someone has been generating loads of emails from my email address hosted here.

I forward all emails to my gmail account. i have changed my gmail account password, easy to do. I cannot figure out what I am meant to do if someone has broken into my email address here .

On gmail it showed that the email address had several failed log in attempts tonight! i can't seem to find out anything more from gmail

Any help much appreciated.