Re: [suse-security] Mailing Trouble ?!

Thanks for the replies. I posted it to SuSE-security because it´s the only SuSE forum I subscribe to, also I believed that my problem might be the result of either an over-eager anti-spam software or my firewall.

Your mx records show 0 router.leat.ruhr-uni-bochum.de 20 mi.ruhr-uni-bochum.de

router.leat.ruhr-uni-bochum.de points to two A records 134.147.162.39 and 134.147.55.1, both of which accept connections on port 25, but just timeout, no error message or anything.

134.147.162.39 is my external NIC, 134.147.55.1 my internal NIC. Communication from outside my domain to 134.147.55.1 is blocked by the firewall, this is intended. Where can I change that so that my servers gives back the appropiate message ? I looked at sendmail.cf but didn´t find anything I deemed useful in that matter. Also, my knowledge of sendmail is pretty limited.

mi.ruhr-uni-bochum.de points to two A records 127.147.64.30 and 134.147.32.86, both of which accept connections on port 25 and give back a 220 message.

I am guessing that because router.leat.ruhr-uni-bochum.de is accepting connections, but giving out a 220 message or any message for that matter, they may well be correct in not going to the backup mx.

So, how come I sometimes have mail communications from and to that specific site, and sometimes don´t ? Also, this mail server has been running continuously for two years now, and I never missed any mail that I know of.

One other quick question, what does this problem have to do with Suse Security???

See above :) Thanks for the help, Jörg

----- Original Message ----- From: "remote" To: "SuSE-Security-Liste" Sent: Tuesday, September 07, 2004 10:07 AM Subject: [suse-security] Mailing Trouble ?!

Hi !

I run a mail server at a university institute. Recently I noticed that mails from and to a certain site disappeared without notification. After mailing to the sysadmin of that site he told me that his mail server software had given up sending mail to my server after having received an error code 421 whichhe says means that the server is temporarily unable to accept SMTP connections. His system seems to be either unwilling or unable to switch to the alternate mail server in my MX records. My problem is, I don´t know if there is anything wrong with my system. As far as I know, this is the only case where my domain had trouble receiving or sending mail. We experience sluggish mail traffic at times here, but according to my university´s computing center that is their problem because their server are running near full capacity. As far as I have been able to find out, my DNS service is configured correctly (Name resolution and reverse resolution work, my MX records are correct and can be accessed from outside) and my domain is not listed on a blacklist. My questions : 1) Is the inability to establish mail communication to and from this specific site my problem or theirs ? 2) How can I check if my system yields this error-code 421 message ? If so, what can I do to correct it ? . My server is a Linux box running SuSE 8.0, sendmail version is 8.12.2.

Thanks for the help,

Jörg