Problems sending emails

Hi there,

We are a little company. We are testing this amazing "Zoho´s Tool" for checking it is a good idea to implemented it in our way of work.
At the moment all look fantastic :)

We have found a bug when we tried to send a email by our business Zoho account (formacionvirtual.info)
I follow this steps:

   1. Create a domain
   2. Validate domain
   3. Create users (I assign an ID an email count and password)
   4. Send email

In the second step, after the validation of my domain, the system give me this message "Mail Hosting Failed"

It is rare because I can recive well and check my messages in the zoho´s account but I can not sent any mail. All my attempts are sent back to me with this message:

A message that you sent could not be delivered to one or more of its
recipients. This is a permanent error. User Unknown :
[andres@formacionvirtual.info]

Received:from 172.31.252.89 (172.31.252.89 [172.31.252.89]) by svwall.zoho.com
    with SMTP id 1233622015008417.9845324561611; Mon, 2 Feb 2009 16:46:55 -0800 (PST)
Message-ID:<11f399a1b1e.-6412324238096915945.7315053172224342021@formacionvirtual.info>
Date:Tue, 03 Feb 2009 01:46:54 +0100
From:secretaria <secretaria@formacionvirtual.info>
User-Agent:Zoho Mail
To:andres <andres@formacionvirtual.info>
Subject:test zoho
Content-Type:multipart/alternative;
    boundary="----=_Part_92_1772746705.1233622014749"from 172.31.252.89 (172.31.252.89 [172.31.252.89]) by svwall.zoho.com
    with SMTP id 1233622015008417.9845324561611; Mon, 2 Feb 2009 16:46:55 -0800 (PST)

Please, could someone help me to find the problem?
Thanks in advanced.