spam being sent from my domain - how do I stop it?

Several times over the past two months, I have received countless (50-100 each occurance)"Delivery Failure" type messages that werebounced back from emails that I did not send. I don't know how the spammer was able to use my domain and send these emails. Also, I have no idea how many spam emails were successfully sent; I can only count the failures.

This concerns me because (a) these spam mails could cause my domain to be blocked by spam filters, even though I didn't do anything wrong; and (b) my site sends out legitimate membership activation emails and password reminders, and I don't want the spammer to cause me to lose my email privledges.

Please advise what can be done to protect my site from future trouble.

Thank you!

 

Thanks Bruce. I didn't see the KB article earlier - it was helpful and explained what i'm experiencing.

Best regards

 

Use SPF records in the DSN of your domain name.


See http://old.openspf.org/wizard.html, it will generate a 1 line of text that will tell SMTP mailservers who is allowed to send email "from your domain".


Then, depending on where you bought your domain name, this should be easy to add that line to the domain name DNS records.

 

I checked the site you provided for SPF. I also have a lot of emails that bounce back do to email forging Can you give an example of how you would do this.

Will this keep these emails from even going out in the first place?

Below is what I have currently set in discountasp.

mysite.com mx1.internetmailserver.net 10 3600 edit delete
mysite.com mx2.internetmailserver.net 10 3600 edit delete

The site you provided says I should have this:

mx1.internetmailserver.net. IN TXT 'v=spf1 a -all'
mx2.internetmailserver.net. IN TXT 'v=spf1 a -all'

Is this how it would be entered in discountasp or should the format be changed?

thanks,

Gil