550 error - mail sporatically being sent and recieved by only some servers - HELP!!!

Hi, i'm extremely desperate here and i'd really appreciate all the help you can give me. i appologise - i cannot post proper links because of the 5 post rule before being able to post links. so bare with me.

i'm able to send and recieve mail to some addresses with success. however i can NOT send or recieve to others for some reason (such servers as Cyberus dot ca). Here are my details.

First the error I have recieved on each message sent to Cyberus dot ca from my email server Concept4 dot ca returns this:

From: mailer-daemon (at) concept4 (dot) ca <mailer-daemon at concept4 (dot) ca>Add to Addressbook
To: <user (at) concept4 (dot) ca>
CC:
Subject: Mail delivery problems
Date: Wed, 7 Apr 2004 21:54:47 -0400

SMTP error occurred while sending message to following recipient(s)
webmaster(at)cyberus(dot)ca
550 Sender verify failed

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my MX is set as so at everydns(dot)net - view attachment for a screenshot of the settings.

You'll notice that i have two A names pointing to my web server and then i have mail(dot)concept4(dot)ca and the MX set to another host on another IP.

Please see the reported readings from dnsreport dot com for concept4(dot)ca:


HELP!
I'm quite sure that the MX settings are ok but who knows maybe i'm missing something here. I've even checked into abuse (dot) net

it says it can't even connect to the server? weird? yah!

If anyone can solve this for me I'll be in your debt since there's a few users that rely on my service and i haven't found a solution for about a week!

 

 

 

 

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