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Thread: [SOLVED] Graylist error

  1. #1
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    Default [SOLVED] Graylist error

    Hi guys, i got this error at the admin report,

    2008-04-24 15:10:20 deferred (host mail.brightcell.net[72.55.164.72] said: 451 4.7.1 Greylisting in action, please come back later (in reply to RCPT TO command))

    It seems that i i'm being graylisting, anyone knows how can i avoid to be graylisted is there a method such as in blackmailing lists? thanks any help

  2. #2
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    In short: It's not a really bad thing, in-fact you might setup greylisting on your server.

    The greylisting/graylisting on the other end isn't something you can control unless the other server's admin adds you to some sort of whitelist or time based auto-whitelist, but do read on:

    A mail transfer agent using greylisting will "temporarily reject" any email from a sender it does not recognize. If the mail is legitimate, the originating server will most likely try again to send it later, at which time the destination will accept it. Most greylisting solutions will then auto-whitelists sucessful domains/IP's somewhere so they don't have to spend time in your graylist hold later on. You can also typically configure the time for this 'auto-whitelist ' to expire. In addition you might permanently whitelist your frequent sender domains.

    If the mail is from a spammer, it will probably not be retried, and spam sources which re-transmit later are more likely to be listed in DNSBLs and distributed signature systems such as Vipul's Razor.
    The basic idea is that the spammer's mail server(s) aren't respecting RFC standards - by sending so many emails, spammers can't afford to spend to much resources on resending emails when they could not be delivered, so they ignore return codes.
    From this idea, greylisting simply rejects any untrusted mail domain by giving a 450 response code, which means "I can't deal with your request now, please try again later".

    In most greylisting solutions, when a request for mail delivery is received by the MTA via SMTP, a triplet CLIENT_IP / SENDER / RECIPIENT is built. If it is the first time that this triplet is seen, or if the triplet was first seen less than x minutes ago (which prevents a spammer from trying 3 in a row in one minute as servers usually wait for 5-10 minutes) then the mail gets rejected with a 450. If the sending server is still trying after x minutes, the MTA accepts the message and could be configured to add the sender information to its auto-whitelist database. So then you would be just seeing a x minute delay the first time they receive a message from a new source.

    Yahoo or see http://Greylisting.org for some examples. There are tons of different greylist programs, for example: Some can be configure so that you hold the mail for up to one hour, (unless they get a reattempt response sooner), and then deliver it anyway with an additional spam score tacked on etc. Thus no mail is really ever lost to accidental greylisting.

    If you'd like to implement greylisting on your end you might start at these community articles:
    Greylisting - Improving Anti-spam system - Zimbra :: Wiki
    Connecting with SQLGrey - Zimbra :: Wiki
    Postfix Policyd - Zimbra :: Wiki

  3. #3
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    Thanks a lot mmorse, it get my picture clear, i'm gonna check the documents yo sent, thanx again

  4. #4
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    Super short version from point-of-view on that error message: Your server will retry to send the message again. Future messages to that address will probably deliver faster as you'll probably be added to some rolling auto-whitelist for 7-30 days.
    ---
    There's even some products out there that can be configured for 'double greylist' - requiring two (or more) attempts before mail is let through.

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