Trinidad,

Spam blocking is often a "religious" discussion!  Please be aware that this response is my opinion only.

First, although I have a similar block, I prefer to block based on the patterns that spammers use to obscure the message (obfuscation) rather that the content itself. This removes any possibility of being accused of "censoring" our customers emails.  The filter you propose, unfortunately also blocks many, if not most lists such as "Yahoo Groups".  I try to use mainly "Regular Expressions" or RegEx's to block and resort to literal keywords only when I can't quite figure out what the pattern is that I want to block.  The keyword that I have that is close to yours is "img src=3D"http://" and it seems to work.  My keyword list is quite small but has been VERY effective.  For reference only, I will post it as follows:

(<[!--]+[\x20]{0,1}[a-zA-Z0-9]{10,}[\x20]{0,1}[!--])
(href="http://+[\d])
(http://.{0,10}%[\d])
(<[!--]+[a-zA-Z0-9]{2}(-->))
((<font color="#ffffff">.*){3,8})
((\|.*){11,})
(content\-type:\x20text/html\r\ncontent-transfer\-encoding:\x20base64\r\n)
(http://www..*.(com|net|org)@www)
((limited time (special|offer)))
pro2ware.biz
text-decoration: blink
98207.biz
herbalpillsonline
pillsavings
red.ecablenetwork.com
horfinc.com
click here to start
thousands of other email providers
gsc-100
img src=3D"http://
is a one time mailing
your privacy is extremely important to us
one of our member sites

I also try to remove some of the Bogus email addresses by detecting address constructs that have been posted as ALWAYS being invalid. My "FromEmail black list looks like:

(\b[\d+]+([\-a-za-z0-9_\.\+])+(@hotmail|@juno)\.com)
(\b[\d]+@(aol\.com|msn\.com|bellsouth\.net|brandeis\.edu))
(\w{17,}@(canada|aol|hotbot)\.com)
((@hello\.com|@veriopt\.com|ha@sexyfun\.net|@himailer.com|clubhotlist@aol.com))
anyone@*
noone@*
friend@*
someone@*
*@gmx.at
*@topprodsource.com
*@myobdeals.com
*@mailseeker.net
offers@
senders@
test*@test.com
*@ultimateoffers.net
*@uc-bulk1.local
@offermania.*
@hotpop.com

Between these 2 lists, very little gets past the filter (along with checking for RDNS and 3 dnsbl lists).  What does get through, I save and when I have "free" time, I try to figure out what the Spamer has done to get past the filters and make adjustments accordingly. As a result, the lists I posted here, may change at a later date.

I hope this helps.

Regards,