Re: help -- nmap not probing filtered ports

[Rob Nicholls <robert () robnicholls co uk>]

On Mon, 11 Oct 2010 21:42:19 -0400, Utkarsh Shrivastava 
<utkarsh12 () gmail com> wrote:
> I've used virtually all the nmap options but not luck. nmap -PN <IP>
> always tells me that the host is up

Did you mean -Pn (although it seems that -PN also works)? This option 
tells Nmap to assume the host is up, so it won't bother checking, and 
therefore will always tell you (unless you're scanning on the local 
subnet) that "Host is up." even if a host doesn't exist.

> I am sure IP x is up because I have received
>  an email within a minute from it. Any pointers?

It might be sending emails, but it might not be configured to receive 
emails (or if it does, perhaps it receives emails from another IP that's 
assigned to the same host). It only needs to have an open port if it 
receives emails.

Another possibility is that firewall rules are only allowing the IPs of 
authorised hosts to send emails, which the host will relay to anywhere, 
which is why the SMTP port looks filtered to you, but you're still able 
to receive emails from it.

Rob

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