Many list admins probably have the problem of spam sent to the request and the mailling list address and forwarded later to the maintainer address. To make things worse the standard SmartList installation will send a help message or a "You are not a member of this list" message to the nonexistent spam address which leads to bounces - again forwarded to the maintainer.
To silently delete most of the spam sent to my mailing list addresses I extended the rc.local.s00 recipe hook which I am using now to sort out certain mail e.g. with attachments or sent as html. The recipe sorted out the mail very well but sent a message to the maintainer and the sender even if it was pure spam. I modified it to check before if the sender is on the accept list(s). If not, the message is silently dumped to /dev/null.
Since most of the spam is sent as html and/or with attachments the spams sent to the maintainer have stopped almost completely. The drawback of this solution is, that if a non member wanting to contribute to the list with a mail attachment he won't get any hint that he has to subscribe before posting. You can find the modified rc.local.s00 recipes attached.
To block the forwarding of spam sent to the request address I am going to use the following recipe in rc.local.r30:
:0 * !^X-Diagnostic: Already on the subscriber list * > 4096 /dev/null
I haven't tested it in production but I am confident that it will sort out all remaining spam. It could create problems if peoples are trying to (un)subscribe with messages larger than 4k which I haven't experienced yet as far as I remember.
Werner