Help Needed: My RHEL5 box suddenly stopped accepting e-mails

Bohdan Sydor bohdan at
Tue May 10 07:08:42 UTC 2011

On 05/10/2011 07:41 AM, Mun wrote:

> Well, unfortunately my IT dept is claiming their network is fine--and
> therefore the problem lies
> either with my system, or is not worth their time to debug.  I am still
> I went ahead and made the changes to the iptables logging as you suggested.
>  When I use swaks to
> send my machine email from an offsite system, I _do_ see messages show up in
> my /var/log/messages
> file showing some kind of interaction between the offsite system and my
> system.  I don't know what is
> being discussed between the systems, but the offsite system does finally
> timeout in it's attemt to connect.

Additionally, you can run from a linux box that is in any external
network the following command:

nmap -p 22,25 yourMachineNameOrIP

The output should be similar to the this:

22/tcp  open  ssh
25/tcp  open  smtp

OR rather to that:

22/tcp open   ssh
25/tcp closed smtp

In the report you would see if ports tcp 22 and tcp 25 are remotely
accessible on the mail system.

>From the other side, run on your mail server that command:

netstat -ntlp | egrep ':2(2|5)'

If the output is like this below

tcp        0      0    *
LISTEN      1105/sshd
tcp        0      0  *               LISTEN

you've got a kind of evidence for your IT dept.


Bohdan Sydor

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