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

[Barry Brimer]

I've not been following this too closely, but I'll make a few suggestions 
in no particular order.

1.  Add an iptables logging rule that logs and connections to port 25 not 
from localhost.  Something like:
iptables -I INPUT -i ! lo -p tcp -m tcp --dport 25 -j LOG

Verify connections (or lack thereof) in /var/log/messages

2.  Is SELinux enabled?  Find out with "getenforce" .. if it is on, turn 
it off temporarily with "setenforce 0" (as root)

3.  Is there anything relevant in /var/log/messages /var/log/maillog 
/var/log/audit/audit.log ??

4.  Make sure you're not out of inodes with "df -i"

5.  Try connecting to the mail server manually from another machine on the 
same subnet.

6.  Verify other Internet communications work .. perhaps you've got a bad 
route of some kind.

7.  Run some tests with swaks <http://jetmore.org/john/code/swaks/>

8.  Use system-switch-mail to verify that your system is using sendmail.

9.  Add a second local IP address to your machine .. test that as well, 
see if there are any different results.

Good luck.

Barry
On Sat, 7 May 2011, Mun wrote:

> Hi   Bohdan,
>
>
> On Sat, May 7, 2011 at 10:21 PM, Bohdan Sydor <bohdan at harazd.net> wrote:
>
>> On 05/08/2011 06:30 AM, Mun wrote:
>>
>>> Does everything above look okay?
>>
>> Yes, they all seem to be alright.
>>
>> Next, let's try to telnet to the smtp port:
>>
>> - from the localhost. Simply telnet localhost 25 and try to submit a
>> sample msg.
>>
>
> You are now beyond my understanding of sendmail.  After telnetting,
> what is the command I should enter?
>
>
>> - from any other machine that is in the same subnet as the mail server
>>
>>
>>> From any other remote hosts we already know that it fails. But do you
>> refer to the MTA by address or by name? Check the DNS entries for the MTA:
>>
>> host -t mx yourDomainName
>>
>
> This returned a name (not an address).  Let say "xyz1.domain"
>
>
>
>> host -t a theResultNameFromPreviousCmd
>> Is it the same IP as assigned to the server?
>>
>
> Yes, the IP does match that of "xyz1.domain"
>
> But this piqued my interest, and when I look in sendmail.cf I see the
> following lines:
> # "Smart" relay host (may be null)
> DSabc1.domain
>
> Should this entry be "xyz1.domain" (to match the the 'host -t mx' command's
> output)?
> Or is it okay that the line in sendmail.cf refers to a different server?
>
> Best regards,
>
> -- 
> Mun
>
>
>
>
>>
>> --
>> regards
>>
>> Bohdan Sydor
>> www.sydor.net
>>
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