reason: 550 Host unknown

[daniel.ao_ironport]

Recently, I've installed a C100 in my company. The email server is SendMail, After I configured SendMail to send email through C100. Some users reported that they got the bounce mail
The original message was received at Wed, 28 Nov 2007 11:14:03 +0800 from [192.168.1.113]

----- The following addresses had permanent fatal errors ----- <gdbm>
(reason: 550 Host unknown)

----- Transcript of session follows ----- 550 5.1.2 <gdbm>... Host unknown (Name server: 192.168.2.4: host not found)

when they sent email to some domains.

But when I configured SendMail to send email directly to the Internet (Bypass C100), users never receive such bounce mail. What's the problem?

[Mark [CSE]_ironport]

Hi,

This error file does not look like it was produced on the IronPort. That looks more like sendmail which cannot resolve the name. Please check if the name resolving from the sendmail server to the IronPort is OK.

If you think the sendmail is contacting the IronPort. Please look inside the IronPort mail logs to see if sendmail can talk to the IronPort.

(http://tinyurl.com/jb7z4)

Cheers,

Mark