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sendmail: reject mail if sender address is invalid
Hi
Is it possible to have sendmail reject mail from a sender that does not have a valid e-mail address and has not been sent from the valid MX for that domain, if possible, gracefully and quiet?
What I am getting at is the following:
If I use the -f switch on sendmail, I can send mail from any of my Linux boxes and "pose" as someone else. Although the trained system admin will immediately see that the message has a "may be forged" or some other tell-tale sign of this, most "novice" users never bother to check the full headers, and simply look at the From: address and sees something familiar and take it as the truth.
I think we have all seen this exploited lately with the "techsupport@microsoft.com
Also, when a spammer sends an e-mail, usually, when you reply to that address, you get a "user unknown" etc message back. And it is THIS that I am wondering about. Can you configure sendmail or some other util to reject mail from a sender if his return address or the server from where he sent the mail is not "valid"?
I think I have asked something similar to this previously, and I *think* the outcome was that *i think* it was not possible to reject on the basis of the valid MX for a domain due to the way sendmail was designed, but I can't remeber, and am almost more interested to know if you could at least do something about a sender that doesn't even have a valid e-mail address to begin with.
Thanks
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by: jleviePosted on 2003-06-06 at 07:59:54ID: 8666782
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