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  1. #1
    Join Date
    Oct 2005
    Location
    Internet
    Posts
    1,134

    Use callouts to verify the existence of email senders.

    Do you guys use this feature? Do you think its a good idea?
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  2. #2
    Even though the practice of using callouts is RFC compliant, in the real world you will run into issues with undelivered email from legitimate users.

    This article gives a pretty good overview of potential problems you may run into while using this feature:

    http://www.tldp.org/HOWTO/Spam-Filte....html#callback

    When we were experimenting with callouts, the email server had rejected messages from two major internet sites, including the domain of a well known datacenter - their support ticketing system was sending messages with an invalid return address. Certainly, it is their fault for being RFC ignorant, but unfortunately this is not uncommon today.

    Also keep in mind that some administrators have setup their email servers to reject "RCPT TO:" requests if the envelope sender address is blank. This will result in your callouts being rejected if you are using exim's default configuration. (Again, rejecting blank sender is a violation of RFC).

    It is up to you to decide whether you want to noticeably decrease the amount of incoming spam plus contribute to the cause of making the Internet a better (standard compliant) place, or to save yourself from otherwise unavoidable and time-consuming problems.

    Technically, unlike with the old argument about RBL usage, the sender's "RFC ignorance" gives you a clear moral right to reject email messages from them.

  3. #3
    Join Date
    Dec 2000
    Location
    Atlanta
    Posts
    574
    Quote Originally Posted by Harmolodic

    Technically, unlike with the old argument about RBL usage, the sender's "RFC ignorance" gives you a clear moral right to reject email messages from them.
    Good point. Problem is, clients don't care about RFC. They want the email to get through, every time.

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