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Interpreting NDRs

By barbara.jones ·
I believe I have relaying properly prohibited on my Exchange 5.5 SP4 (W2000) server because when I test it via telnet, it denies relaying. However, I am still receiving several NDRs that make me think somehow the relays are still getting through. Examples:

550 Requested action not taken:user account inactive
550 Relaying is prohibited
550 <***@***.com>... User unknown
553 VS10-RT Possible forgery or deactivated due to abuse

TIA!!!

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Interpreting NDRs

by canucker In reply to Interpreting NDRs

this is telling you that in fact your server is prohibiting relaying.

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Interpreting NDRs

by barbara.jones In reply to Interpreting NDRs

Poster rated this answer

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Interpreting NDRs

by barbara.jones In reply to Interpreting NDRs

Because the 550's all returned different comments, I assumed the comments were returned from the destination servers so I thought the e-mails were getting through. Is that not the case or how does that work?

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Interpreting NDRs

by brasslet In reply to Interpreting NDRs

Let's see if I can explain this clearly -- if not clear, send me an email and I'll do my best to clarify.

The most likely cause for these destination-generated NDRs is that your server (like every other mail server connected to the Internet) is the target of spam. I don't mean that you're being used as a relay. Rather, there are spammers that are targeting user accounts that resolve to your domain and mail server. Because this junk mail is generated by various means, many of the accounts that are sent this spam are deleted or never existed. Even if the account isn't there, though, you server receives it (as it should) and then generates an NDR of its own.

Most spammers spoof or use a bogus From: address so when your server does its job and sends the NDR to the from address in the message header, you get an NDR from the destination side.

Quite a pain, this junk mail. Look at all the traffic generated, to no useful end.

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Interpreting NDRs

by barbara.jones In reply to Interpreting NDRs
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Interpreting NDRs

by barbara.jones In reply to Interpreting NDRs

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