postfix resolve problem

[Rixcz]

Hi, If I want sent mail on someone server, I recieved this:

---

This is the mail system at host rxx.cz.

I'm sorry to have to inform you that your message could not
be delivered to one or more recipients. It's attached below.

For further assistance, please send mail to postmaster.

If you do so, please include this problem report. You can
delete your own text from the attached returned message.

The mail system

<fixxt@xx.cz>: host mail.xxx.cz[194.x.x.x] said: 501 5.7.1
<dxxa@xxx.cz>... Sender IP must resolve (in reply to MAIL FROM
command)

--------------------------------------------------------------------------------


Received: from dilna (ip-85-1xxl.cz [85.160.78.xxx])
by r01.rhost.cz (Postfix) with ESMTP id AA23C2144056;
Mon, 13 Jul 2009 15:04:53 +0200 (CEST)
Message-ID: <001201xx27a60a@xxa>
From: "dilna" <dixxa@xx.cz>
To: <fiat@axxxa.cz>
Cc: <exxan@sxxm.cz>
Subject: =?iso-8859-1?Q?Duc=E1to?=
Date: Mon, 13 Jul 2009 15:04:47 +0200
MIME-Version: 1.0
Content-Type: multipart/mixed;
boundary="----=_NextPart_000_000D_01CA03CB.43862670"
X-Priority: 3
X-MSMail-Priority: Normal
X-Mailer: Microsoft Outlook Express 6.00.2800.1106
X-MimeOLE: Produced By Microsoft MimeOLE V6.00.2800.1106
X-Antivirus: avast! (VPS 090712-0, 12.07.2009), Outbound message
X-Antivirus-Status: Clean

--

ps: I use ISPconfig 2

Any idea? thx

[abix_adamj]

Change Reverese DNS for your Server to something, which looks like a server.

Adam