Forum Discussion

BigDog7's avatar
New Contributor
5 years ago

Cox has marked my email server as a spammer - how to resolve?

I am using Siteground Hosting for my business websites and email addresses.  Cox has recently marked my email server's IP address as spam.  At least I am getting non deliverable notices from Cox.  I have tried from 2 separate email addresses and both have the same failure notices.  Here is a copy of the message with personal info redacted:


Reporting-MTA: dns;

Action: failed
Final-Recipient: rfc822;
Status: 5.0.0
Remote-MTA: dns;
Diagnostic-Code: smtp; 421 cmsmtp blocked. Refer to Error Codes section at for more information. AUP#CXCNCT: retry timeout exceeded

The email server ip address that is being blocked is and does not show up on any spam blacklists that I can see.

I can give you the email addresses if you need them, but do not want to post them to a public forum.

9 Replies

  • PC_Medic's avatar
    New Contributor II

    Have the same issue at my employer where I am the I.T. Coordinator. This (421 #CXCNCT) error is not due to a 'blacklist' block, but due to too many concurrent connections being attempted. Cox tells me it is a Siteground configuration issue and Siteground says it is a Cox issue.

    Now at first I was thinking it may have been caused by staff sending out 'group' emails even though they were adhering to the <40 recipients in a group rule. However I have tested myself by trying to send a single email from my work accounts ( I have 3) to my home account and get the error about 80% of the time. The annoying part is it sometimes takes 2 to 3 days to get the bounce back message from Cox.

    Too make things even more interesting, in many cases I (and others) actually receive the emails that Cox's server is saying failed to be delivered.

    • BigDog7's avatar
      New Contributor

      Thanks for the info.  Cox is the only ISP that is complaining.  My wife does send some group emails, but never more than 15 recipients.  We can send emails to many other domains without the issue.  It should be simple for Cox to review the emails from our server and if they don't see anything nefarious then whitelist the server.

      You mentioned a 40 recipient rule - does Cox have a page detailing this and other requirements in enough detail that I can send to Siteground support?  It would be best to have a tech from each company talk directly.

      • chiefkibitzer's avatar
        New Contributor II

        OMG. I have been dealing with EXACT nightmare for a month and half and still no resolution. Siteground blames Cox and vice versa. Siteground claims they are requesting to be delisted from Cox and Cox won't respond. When I call Cox they just escalate the support to a higher tier and promise a call back which never happens. I am beyond frustrated. Cox is a local company and all the email addresses on my server (dozen domains) correspond with people who use Cox cause they're local. And of course now all the Siteground emails are being blocked or delayed by Cox. Occasionally 1 or 2 will go through but even that's rare. PLEASE, if anyone gets a resolution to this please post.