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Exim Spam Concern

Discussion in 'General Discussion' started by PeteC, Aug 16, 2006.

  1. PeteC

    PeteC Well-Known Member

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    I just discovered today that I can send e-mail without SMTP authentication or POP-before-SMTP (using antirelayd) on any server, if these two requirements are met:

    1) The "From:" address is a valid e-mail account (not just a forwarder).
    2) The "To:" address is valid and its domain resides on the same server as the "From:" address.

    This seems like a very serious loophole for spammers, because armed with the address of a valid e-mail account at a specific cPanel-hosted domain, they could then spam all day long to addresses at that domain or even at other domains on that same server.

    I'm hoping I've missed something here, but I tested and re-tested on multiple servers and the above description seems accurate.

    I haven't even dug into exim.conf yet to see why this is allowed or how to block it. But I thought I should go ahead and post this possible loophole so others could correct me if I'm wrong or add any insight of their own.
     
  2. chirpy

    chirpy Well-Known Member

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    That's perfectly normal behaviour for an SMTP server, otherwise you would never receive any email - it's simply relaying email into the server addressed to a valid recipient.
     
  3. PeteC

    PeteC Well-Known Member

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    So then the only protection against spammers in that case is SpamAssassin, RBL, etc.?
     
  4. chirpy

    chirpy Well-Known Member

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    Yes, indeed.
     
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