Forum Discussion

frustrated's avatar
New Contributor
5 years ago

Hey, @Cox technical people, something in your filters have changed!

I am beyond frustrated with spending hours on the phone over the past week with Cox reps who cannot solve this, and are unwilling to escalate to real technical IT people who can. It's not an Outlook problem! If I had a choice, I'd have already dumps Cox. Eventually, the Cox monopoly will evaporate and people will remember their lack of customer support.

I have used the same email address and Outlook setup for years. It has worked (until last week). Now, I cannot send an outbound email via outlook, When I do, here is the bounce back email response I get:

From: System Administrator

To: Me

Subject: Deliverable: Test

Your message did not reach some or all of the intended recipients.


      Subject:    Test 

      Sent: 5/23/2020 9:00 AM


The following recipient(s) cannot be reached:


      '' on 5/23/2020 9:00 AM

            550 <> sender rejected. Refer to Error Codes section at for more information. AUP#CXSNDR

And, the 550 error code on the COx website says:

"550 - [<mailfrom address> sender rejected] - Cox requires that all sender domains resolve to a valid MX or A-record within DNS. - Ensure that your domain has a valid MX or A-record within DNS.


Anyone have any ideas?

4 Replies

  • bearone2's avatar
    Contributor III

    office '97 on floppies, yeah i go back with outlook.

    i've still got outlook 2002 on an xppro machine, so i've been using outlook(current 2016) quite a while.

    yes, some aren't delivered because outlook has always/will always, protect the client.

    i send so many emails now-days, yes some are political, no biggy for me if a few don't get delivered.

    take a breath!!

  • Capitalidea's avatar
    New Contributor

    My emails are getting blocked as well with 550 code.  It's a small group where we discuss geopolitical news of the day.  I believe this is censorship similar to what Facebook, Twitter, and u tube are doing. Did yours get lifted?

    • ChrisL's avatar
      Former Moderator
      Do you have the full text of the error you're getting?

  • Hi, I understand it can be frustrating when you are unable to reach a recipient with an email. The error code is listed on our website: If you are having problems with email delivery send us an email at for assistance. Your email must contain all of the following information in order for us to process your request.

    First name
    Last name
    Email address
    Phone number
    IP/CIDR range of outgoing email servers

    From the following choices, indicate the item that best describes the issue you are experiencing.
    My IP address is being blocked
    My domain is being blocked
    My email is being marked as spam
    My email is not arriving to the intended recipients
    My email is being delayed

    Include a detailed description of the issue you are experiencing, such as the date and time when the problem began and the corrective action that has been taken.

    Include email server logs related to the issues.

    Note: Due to the technical nature of the requested information, this email should be submitted by an email administrator or other technical contact that is familiar, and can obtain, all of the requested details.

    Thank you,

    Mike J.
    Cox Support Forums Moderator