return confirmation is quite a good one.
someone sends an email, it gets autoresponded adding a header like [not jnk 37239847] or whatever with a polite message something like:
"due to overwhelming amounts of sp&m mail, please simply reply to resend this message to prove you are a genuine sender"
that way your filters can respond to the added header and while it doesnt junk it outright can at least prioritise it above the rest. As spam is automated and unlikely to reply it would help filter out the shite. Also, as each header is unique and changeable it would at least outwit the bots.
Still a pain in he arse for everyone concerned though.
someone sends an email, it gets autoresponded adding a header like [not jnk 37239847] or whatever with a polite message something like:
"due to overwhelming amounts of sp&m mail, please simply reply to resend this message to prove you are a genuine sender"
that way your filters can respond to the added header and while it doesnt junk it outright can at least prioritise it above the rest. As spam is automated and unlikely to reply it would help filter out the shite. Also, as each header is unique and changeable it would at least outwit the bots.
Still a pain in he arse for everyone concerned though.