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coxfiberuser-ph's avatar
New Contributor
4 years ago

AUP#CXSNDR error when sending email

I am a Cox Gigablast user in Phoenix, AZ.  Since Wednesday, May 20, 2020, I am no longer able to send email from Mozilla Thunderbird using a third party email (  This has been working for many years and I didn't make any software changes recently.  I also have all the latest versions and patches of Windows and Thunderbird installed.
The error I am getting in a popup after I send the email is

An error occurred while sending mail. The mail server responded:  <> sender rejected. Refer to Error Codes section at for more information. AUP#CXSNDR. Please check the message and try again.

I am using the following SMTP config:   port 465   Normal Password    SSL/TLS

5 Replies

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  • ChrisL's avatar
    Former Moderator
    This error indicates that the origin email system may not have an SPF record configured to allow our SMTP server to send email using their domain name. If they offer secure SMTP connections you may want to try configuring your email client to use their outbound server to see if that helps.

    • jredwolf's avatar
      New Contributor

      what does this mean?  I have sent similar messages to the same address list for years.

      what is a spf record?  It's all cox; via thunderbird. 

      • ColleenD's avatar

        jredwolf I'm sorry to hear you are having trouble. Are you seeing the CXSNDR error when sending with your Cox email address? If so, please email us at with your name, address, description of the problem and a link to your  forum post. If you are having trouble with an email address from another domain, I recommend reaching out to the provider of that email address for assistance. 

  • jonjon34t's avatar
    New Contributor

    I am having the same email sending issue and error message that also started about 5 days ago, in Orange County, CA.  Apparently, COX recently made it so you can't send emails using non email addresses. Grrrr.

    • LisaH's avatar
      Hi Jonjon34t. In order to send an email from a Cox email server, you need to use a cox email account. - Lisa, Cox Support Forums Moderator