Deleting large numbers of comments is Really Really Annoying.
Above the comments display, alongside the hide link, add a bulk delete link. Clicking this link redisplays the page, but gives each comment a "delete" checkbox. When the checkbox is ticked, the comment changes colour to show it's been selected.
At the bottom of the page, there's a big delete button that removes all highlighted comments at the same time.
if comments are mass-deleted only a single email should be sent, summarising the deleted comments.