SpamCop FAQ : General information about SpamCop : Non-SpamCop information :
.. that spammers add to the subject line, or to the very bottom of the spam?

To befuddle the automatic spam cancel bots that rove Usenet and cancel byte-for-byte postings for every message/email. Every number changes on every post, but nowadays, some intelligent administrative tools can recognize those numbers and cancel those spams.

Basically, the codes are intended to to confuse the autocancel comparison tools that the good guys use.

The same applies to email.

As more and more ISPs and individual users put email spam filters in place, spammers try different tricks to fool the filters. You may notice a string of numbers in the subject line, random numbers or characters in the body text, or even a rambling of words that may or may not make sense.

It is not believed these methods are used to identify recipients in any way. Rather, they are used to try to trick spam filters into thinking each message is unique in content.
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