...since the header gets deleted and is instantly replaceable blocking spam by Ip addresses would be useless.
If someone is attempting to block SPAM using this single technique then they are pretty dopey or they've had their head in the sand for a long time. For the past few years SPAM filters have used a concoction of techniques to filter SPAM which makes header forging much less effective. One factor in all of this is ISP mail server Port 25 blocking and/or mail server spam filters. This limits the effectiveness of using faked or forged email headers, IPs or email domains with no MX Records.

This leaves the following avenues open for SPAMMERS:

* Use throw-away email domains (with fake, forged or stolen ids)
* Use throw-away free email addresses (with fake or stolen ids)
* Use throw-away ISP access accounts (with forged or stolen ids)
* Hijack mail servers
* Hijack PCs by installing Spam Zombies
* Open relay mail servers around the world
* Using a filter-evading script that randomizes subject lines, source addresses and entire domains to avoid or make it harder to be identified as bulk emails
* Using programs that automatically randomize different internet access accounts and then quickly log out


Anyway...

--TH13