In the control panel, on the left hand side is a menu option titled:
Sender Policy Framework
If you never send outgoing mail from that domain, you can put a checkmark next to the domain, and make sure the pulldown box says:
Checked domains *NEVER* send e-mail.
Click Apply Status, and at the top of the hour, your DNS will be updated.
If you do send email from that domain, but use our SMTP server:
Checkmark the domain, pull down the select box and select the option that says:
Domain sends email *ONLY* from the IP assigned to it
Click Apply Status, and at the top of the hour, your DNS will be updated.
If however, you send email from your ISP, i.e. comcast.net, etc.
Click, Set up a new Rule Profile
The first option determines what to do if someone else is using SPF, typically you'll want to choose the last option of:
(-) hard fail: Email not sent from the IP in the ruleset is forged.
If you send email through your ISP (i.e. qwest.net or rr.com), then the next field needs to contain that domain.
In the next field there should be a link below the field with the machine name (or names) that you are on. Click each one that can send mail out from that domain.
Click Submit NEW PROFILE RULE
You'll be returned to the previous screen, but, your new rule will show up in the select box. Checkmark the domain, pull down the select box and select the option that says:
v=spf1 DOMAIN_IP_ADDRESS etc etc
Click Apply Status, and at the top of the hour, your DNS will be updated.
Or, you can hit us on ICQ, Live Support, email, trouble ticket. I only posted because I vaguely recall seeing a trouble ticket go through regarding spam and I think you might have submitted the ticket?
For those of you wondering what is going on:
Spammers send emails out using email addresses that have been seen in mailboxes of trojaned/hijacked computers. Often times, if you have sent email to someone, and they are infected, your email address will get used as an outgoing address under the presumption that someone might vaguely recognize the address and give the spammer a little glimmer of hope that his email will be read. Unfortunately, the mail never comes from you, often times you don't even know it has been sent until you start seeing the bounces. Those bounces are typically called backscatter.
The theory is, if they use a random domain name or a domain name that has sent to some of their recipients, it will bypass the spam filters. Often, but not always, spammers do check to see if there are restrictive SPF records on the domain to give the maximum chance that their email will go through.
For those more curious about the details of how SPF is supposed to work:
http://www.openspf.org/