Thanks for your quick response Michael, But I don't understand what can make my server a backscatter source.
I'm not relaying from outside, and I only accept messages from my domain, and only from my aging sendmail+dovecot server, so no relaying from outside. What I don't have is what you said: check for local recipients. But this is a problem? Thanks in advance, On May 14, 2012, at 2:22 PM, Michael Orlitzky wrote: > On 05/14/12 12:38, Vinícius Ferrão wrote: >> Hello, >> >> I'm running a postfix mail filtering gateway in a hardened gentoo box >> and I really don't know what to do with double-bounced messages. >> >> Since we have a lot of spam bots attacking our infrastructure, the >> double bounce messages cannot be ignored and mail mail queue is growing >> with undeliverable double bounce messages. >> >> Any thoughts on what should be done to handle this? >> > > If you are accepting mail for addresses that don't belong to you, stop! > That makes you a backscatter source, and will eventually (rightly) get > you blacklisted. > > You said it's a mail filtering gateway... Usually the reason people > backscatter on a gateway is because "it's hard" to get a list of all > valid recipients; usually those recipients are on some other mail > server. There are ways to do it, though, and you must, e.g. > > a) Run a cron job that pulls valid accounts every hour. > > b) Store the email accounts in a database, and allow the gateway to > query the database to determine which users are valid. > > c) Use recipient verification[1]. When receiving mail, your gateway > can open a connection to the real mail server in the background, > and see if the recipient is valid. > > > We use a combination of all three. We use (a) for an old Windows box, > (b) for users stored in Dovecot, and (c) for customers with their own > Exchange servers. > > If you ask over on postfix-users and provide the output of `postconf > -n`, there are plenty of people who are able to give you tips relevant > to your specific configuration. > > > [1] http://www.postfix.org/ADDRESS_VERIFICATION_README.html#recipient > >
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