large email queues

[Aasef Iqbal <aneedz gmail com>]

Hi!

I am working with a hosting company. One of our servers is being to
SPAM. I can see large number of emails being sent to few particular
domains. The sender is either <> or <anonymouse mydomain com>

There are two question I am looking for help.

1. How can I remove the emails already in queue. with blank sender
address or <anonymouse xyz com> as sender address, or even the domain
name pointed in TO address.

2. as I am we provide hosting, I doubt some of my clients shall
probably be running some scripts to generate these emails... How can I
verify this.

Please comment.

Asif