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



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 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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