I'm flirting with the idea of hosting secondary MX records for a few clients, or asking the ISP to set it up to hold the email. I've had one ISP outright decline the idea, but I think there was technical incompotence involved there :). My question is about security and anti spam.
If the main mail sevrer is down and I set up a second MX record that pointed to my mail server to relay or hold the mail until their service came back up, how can I secure it so spammers can't send mail? I mean, wouldn't they be able to just send a mail through me with any [EMAIL PROTECTED], since it can't contact the main mail server to check whether its allowed? Any tips/URL's on the subject would be most appreciated.
TIA
