Long ago, some mailing list people found that some newbies, rather than
properly UNSUBSCRIBE, after sending a message directly to the list saying,
"UNSCRIBE ME", would then proceed to mark their incoming messages from the
list as "SPAM" in order to stop receiving them. GOOGLE, would of course,
see that a certain address got marked as SPAM by several people, so GOOGLE
would then classify messages from those addresses, disunirregardless of
recipient, as SPAM.
List owners would plead with people to UNSUBSCRIBE properly, and to not
mark messages from the list as SPAM, and even to periodically go to your
SPAM folder and mark list messages as "NOT SPAM".
GOOGLE would further assume that ALL messages with any address from a
given domain should be sorted the same, unless the domain was one of the
ones on their list of BIG domains. If you are a small domain, one
classification might get applied to entire domain, rather than just one
address within the domain.
Often, even the sorting would be done by the address or domain in the FROM
line, rather than the actual IP address where it originated. Thus, a
spammer who spoofs a valid email address can cause the legitimate owner of
that email address to struggle to get out of being classified as SPAM.
--
Grumpy Ol' Fred cisin at
xenosoft.com