Bazooka Joe a écrit : > Last week I got a client that wanted me to spam virii filter for their > in house exchange server. > > I changed the mx from mail.domain.tld (their exchange) to > mail2.domain.tld (my sa box) which relayed to mail.domain.tld. > > Last week all worked as expected. The hundreds of spam droped to 0; > until this weekend. Looking at the headers, mail is going directly to > the mail.domain.tld even though it isn't listed as mx anywhere. > > I can tell the exchange server to only except mail from my server but > has anyone else experienced this? >
many systems cache dns results beyond expectation: - my ISP (free.fr) uses qmail, and I have already seen mail returned after 5 days because the MX wasn't reachable, eventhough the MX was fixed long ago (and test messages were sent after fixing the MX...). I have no idea whether this is because qmail is broked or whether my ISP setup is borked. - some mobile gateways (SFR, aka vodafone-fr) cache negative dns responses eternally (well, at least for more than two months). given that, why would a ratware implement dns correctly?
