mail from my domain blocked by Comcast

I am setting up email for my small business. Our domain is hosted with another company, but we want to use Zoho for our domain email. I have updated the MX records with our domain host, and now I am able to send and receive email from the Zoho/domain email.

I encountered a problem today, in sending to my personal email @comcast.net. Apparently, the number of emails I have sent back and forth have caused Comcast to flag the activity as spam. The error message I received gives a link to a Comcast site where I can get the flag removed. The error message follows below:

This message was created automatically by mail delivery system.

THIS IS A WARNING MESSAGE ONLY.

YOU DO NOT NEED TO RESEND YOUR MESSAGE.

The original message was received at Mon, 18 Jul 2011 16:39:34 -0700
from david.gleason@illuma-keep.com [david.gleason@illuma-keep.com]

----- The following addresses had fatal errors -----
[Status: Error, Address: <david.gleason@comcast.net>, ResponseCode 421, , imta29.emeryville.ca.mail.comcast.net comcast 72.5.230.103 Comcast Blocked for spam. Please see http://help.comcast.net/content/faq/BL000000]

Message will be retried for 4 more day(s)

----- Transcript of session follows -----

Received:from 172.29.248.239 (172.29.248.239 [172.29.248.239]) by mx.zohomail.com
with SMTP id 131101735449030.215511652325745; Mon, 18 Jul 2011 12:29:14 -0700 (PDT)
Message-ID:<1313eb94426.1408855311188855029.-4172862297639206055@illuma-keep.com>
Date:Mon, 18 Jul 2011 12:29:14 -0700
From:David Gleason <david.gleason@illuma-keep.com>
User-Agent:Zoho Mail
To:"david.gleason(david.gleason)" <david.gleason@comcast.net>
Subject:test
Content-Type:multipart/alternative;
boundary="----=_Part_34469_167459607.1311017354276"

In viewing the site at help.comcast.net, they ask specifically for the IP address of the email server, which I do not have. The specifics of what they need are as follows from their website:

It is important that your email administrator is aware of their outbound spam problem to avoid being blocked by Comcast in the future. When contacting your email administrator, you should include the error message contained in the email which alerted you to this problem. This error message contains important information to help your email administrator resolve this issue. Removal requests can be sent to www.comcastsupport.com/rbl and will require the IP address of the blocked mail server (you can get this from your email administrator). Requests submitted through this form are monitored 24 hours a day, 7 days a week to ensure a timely response.

Please provide me with the IP address so I can submit the request to Comcast to unblock our domain from sending to Comcast email addresses.

Thanks