At the least a dedicated IP; I'm a little fuzzy on how easy it would be to tell that two things were on the same physical box as opposed to just the same data center if they have separate IPs; that's a level of forensics a little beyond my expertise.
Even though my buddy's running his own mail server and gets to make his own rules, the straight-up blackholing of suspected spammers is helpful because it's basically a "woops, there's no mail server there anymore" message, rather than a "there's a mail server here but it says Talk to the Hand b/c the inbox ain't listening" (an explicit hard bounce message) or a "Heyyyyyyy we got your email bro!" (accept and send to spambox). Spammers who get a "heyyyyyyyyyyy we got your email bro!" will increase the amount of spam they spray at that server, since it's just indicated it's a possible target. So he's made that choice deliberately and from an informed place. Unfortunately this time it did in fact catch legit mail. So he sent the relevant information along to the agent so the agent could give it to his IT guy to go talk to the blacklist maintainers and get un-blacklisted.
Re: Oh, wow
Even though my buddy's running his own mail server and gets to make his own rules, the straight-up blackholing of suspected spammers is helpful because it's basically a "woops, there's no mail server there anymore" message, rather than a "there's a mail server here but it says Talk to the Hand b/c the inbox ain't listening" (an explicit hard bounce message) or a "Heyyyyyyy we got your email bro!" (accept and send to spambox). Spammers who get a "heyyyyyyyyyyy we got your email bro!" will increase the amount of spam they spray at that server, since it's just indicated it's a possible target. So he's made that choice deliberately and from an informed place. Unfortunately this time it did in fact catch legit mail. So he sent the relevant information along to the agent so the agent could give it to his IT guy to go talk to the blacklist maintainers and get un-blacklisted.