My Forum is having some strange emailing errors

[Nickbe]

It seems like the emails my forum is sending out are not going through at all. These are mostly thread subscription emails they keep bouncing back to me. One suggests the IP has been blocked for spamming but I have never even sent out a mass emails from this email.

Also I am assuming that all the membership activation emails are going straight through since I haven't got any complaints.

So why would activation go through but not the others? and most importantly HOW DO I FIX THIS?

Hi. This is the qmail-send program at qmail-cgi-bulk-0.netfirms.com.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<removed email>:
Sorry, I wasn't able to establish an SMTP connection. (#4.4.1)
I'm not going to try again; this message has been in the queue too long.

--- Below this line is a copy of the message.

Return-Path: <removed email>
Received: (qmail 60611 invoked from network); 18 Aug 2007 20:40:48 -0000
Received: from unknown (10.8.8.6)
by 0 with QMQP; 18 Aug 2007 20:40:48 -0000
Date: 18 Aug 2007 20:40:48 -0000
X-IP: 86.140.149.204
X-URI: /forums/index.php
X-ID: 2835868
To: removed email
Subject: Reply to thread 'The three word game'
From: "Forums" <removed email>
Auto-Submitted: auto-generated
Message-ID: <removed>
MIME-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 8bit
X-Priority: 3
X-Mailer: vBulletin Mail via PHP

and this one is a little different

Hi. This is the qmail-send program at qmail-cgi-norm-0.netfirms.com.
I'm afraid I wasn't able to deliver your message to the following addresses.
This is a permanent error; I've given up. Sorry it didn't work out.

<removed@comcast.net>:
Connected to 204.127.225.26 but sender was rejected.
Remote host said: 550 66.244.250.57 blocked by ldapu=rblmx,dc=comcast,dc=net ->
Blocked for abuse. This IP has been identified for sending large amounts of spam to
the Comcast network. Please contact your Email Service Provider for assistance.

--- Below this line is a copy of the message.

Return-Path: <Removed Email>
Received: (qmail 14517 invoked from network); 20 Aug 2007 02:56:22 -0000
Received: from unknown (10.8.8.30)
by 0 with QMQP; 20 Aug 2007 02:56:22 -0000
Date: 20 Aug 2007 02:56:22 -0000
X-IP: 71.197.131.224
X-URI: /forums/register.php?do=addmember
X-ID: 2835868
To: removed@comcast.net
Subject: Action Required to Activate Membership for Forums
From: "Forums" <Removed Email>
Auto-Submitted: auto-generated
Message-ID: <removed>
MIME-Version: 1.0
Content-Type: text/plain; charset="ISO-8859-1"
Content-Transfer-Encoding: 8bit
X-Priority: 3
X-Mailer: vBulletin Mail via PHP