Попытался тут переслать письмо с одного адреса моего домена на другой. И получил такую гадость:
This message was created automatically by mail delivery software.

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. The following address(es) failed:

xxx@mydomain.com
This message has been rejected because it has
a potentially executable attachment "
=?windows-1251?Q?=C2=F1=E5=F0=EE=F1=F1=E8=E9=F1=EA=E8=E9?==
?windows-1251?Q?_=EA=E0=E4=F0=EE=E2=FB=E9_=EA=EE=ED=E3=F0=E5=F1=F1?= .eml"
This form of attachment has been used by
recent viruses or other malware.
If you meant to send this file then please
package it up as a zip file and resend it.

------ This is a copy of the message, including all the headers. ------

Return-path: <yyy@mydomain.com>
Received: from [127.0.0.1] (helo=www.zuchka.com)
by gamma.deserv.net with smtp (Exim 4.24)
id 1C6qCA-0009dR-6v
for xxx@mydomain.com; Mon, 13 Sep 2004 16:44:34 +0400
Received: from 213.247.199.100 (proxying for unknown)
(SquirrelMail authenticated user info@zuchka.com)
by http://www.zuchka.com with HTTP;
Mon, 13 Sep 2004 16:44:34 +0400 (MSD)
Message-ID: <1757.213.247.199.100.1095079474.squirrel@www.zuchka.com>
Date: Mon, 13 Sep 2004 16:44:34 +0400 (MSD)
Subject: test
From: yyy@mydomain.com
To: xxx@mydomain.com
User-Agent: SquirrelMail/1.4.2
MIME-Version: 1.0
Content-Type: multipart/mixed;boundary="----=_20040913164434_91079"

Запакуйте файл в .zip, например.
Настройки нашего почтового сервера не позволяют принимать почту с исполняемыми файлами, дабы не способствовать распространению вирусов.