Forum Discussion

LPCaillouet's avatar
LPCaillouet
New Contributor
2 years ago

Cox SMTP Access Blocked for Vacation Home IP Address

Cox is the ISP at home in Louisiana.  On Cox WiFi there, I am successful in using either Microsoft Outlook on my Windows 10 laptop or Mail on my iOS 15.7 iPhone (with cellular data either on or off) to receive and send my Cox e-mail.  I use Cox’s recommended settings …
  Incoming:  pop.cox.net / port 995
  Outgoing:  smtp.cox.net / port 465 / SSL

My Problem ...
I also am a customer of Suddenlink (now Optimum) as my ISP at a vacation home in Arkansas and have a Suddenlink-provided modem/router.  My incoming Cox e-mail works fine through Suddenlink WiFi, however I cannot successfully send Cox e-mail through WiFi from Outlook, nor from my iPhone if cellular data is turned off.  This failure occurs from two different devices and two different software platforms, and only occurs when I am using Suddenlink WiFi.  Here is the error message from Outlook I get when trying to send outgoing e-mail …

“Task '... Sending' reported error (0x800CCC6F): 'Your outgoing (SMTP) e-mail server has reported an internal error.  If you continue to receive this message, contact your server administrator or Internet service provider (ISP).  The server responded: 554 cxr-obgw-5003a.stratus.cloudmark.com cmsmtp [my IP address appears here] blocked.  Refer to Error Codes section at www.cox.com/.../email-error-codes.html for more information. AUP#CXDNS”

Why is Cox SMTP blocking my IP address?  Was the prior user of this Suddenlink-provided modem/router on a blacklist?  How can I remedy this?  Who can remedy this?  Prior chats with Cox have led nowhere!  Any advice?

20 Replies

  • Darkatt's avatar
    Darkatt
    Honored Contributor

    Like WMO suggested there are things that need to be checked. It's also possible that someone who previously had the IP address your vacation home is now using, had an infected computer and the IP is listed on a block list, as well as possibly having used that IP to send out spam, again, something that would have it placed on a block list. What is the IP address? We can look up on mx toolbox or spamhaus and other lists to see if there is a problem. We can also look up the dns on the IP and see if it has all the proper records associated with it. 

    • WiderMouthOpen's avatar
      WiderMouthOpen
      Esteemed Contributor
      What is the IP address?

      I was going to ask that, but thought privacy prevented it. Speaking of IP, I wonder if OP could change their IP address by changing the WAN MAC address on the router and rebooting the modem. I think that works on Cox but I wonder if it works on Optimum? Delisting a blacklisted IP address is better IMO, but changing your IP in hope for one that isn't blacklisted is still a option. Then again that would do nothing if ALL the IP address by the ISP have no PTR.

  • WiderMouthOpen's avatar
    WiderMouthOpen
    Esteemed Contributor

    First, see thread here on similar issue. You may want to post there too to broaden awareness.

    The first thing to do is make sure your vacation IP isn't on any blacklists. You can find your IP by googling "what is my IP address" or go to IPChicken.com. To check that IP against blacklists go here. If on a blacklist there are procedures to get off. Some delistings are easier then others.

    After that you also have to make sure that IP address has a PTR record. That is more a luck of a draw kind of thing since there isn't much you can do if your ISP doesn't list their IPs. You could set up a VPN between your home router and vacation router and router the traffic that way but that depends on hardware.

  • LPCaillouet's avatar
    LPCaillouet
    New Contributor

    Yes, my IP address is on a blacklist.  I knew that already.  It has been blacklisted ever since Suddenlink (now Optimum) installed it.  How do I get off?

    • Darkatt's avatar
      Darkatt
      Honored Contributor

      It depends on the blacklist, If it's on the SORBS, ignore it, everyone else does. Sorbs is useless. Another blacklist simply prevents you from running a mailserver from that IP address, but doesn't impact sending mail through a legitimate mailserver, so it really does depend ON the black list you are on. 

    • WiderMouthOpen's avatar
      WiderMouthOpen
      Esteemed Contributor
      Spamhaus ZEN

      Look up your IP address here. It should show options for delisting. I checked mine and has a PBL listing which isn't anything to worry about. Did you check that your IP has a PTR?

  • LPCaillouet's avatar
    LPCaillouet
    New Contributor

    Thanks for pointing me in the right direction.  My IP address is on Spamhaus ZEN PBL list.  One suggestion was to turn on SMTP authentication, but I had already enabled that in my outgoing mail settings in Outlook so that must not be the problem.  There's a lot more to read and digest on the Spamhaus FAQ page.

    Sorry, but I don't know about checking whether my IP address has a PTR -- not even sure what that is?

    Seems to me as though Suddenlink didn't clear my modem/router's IP address from there "not yet installed" list when they install it for me?

    • WiderMouthOpen's avatar
      WiderMouthOpen
      Esteemed Contributor
      not even sure what that is?

      PTR is the reverse look up for your IP address. Imagine IP addresses are like phone numbers and domains are people's caller ID info. Normally, DNS works by looking up the IP address for a domain so you can go to the website, kind of like calling 411 for a person's phone number. A PTR is used when you want to see the domain registered with a IP, like looking up a person's name if you had their phone number. Does that make sense? If not, try reading here.

    • WiderMouthOpen's avatar
      WiderMouthOpen
      Esteemed Contributor

      Yea, that's a problem. No amount of blacklist removal will fix that. Think you are stuck using webmail when away from home. I would suggest creating a email with another carrier to use when away. Something like Gmail or Proton. I don't have any experience with sending with them without a PTR but it's worth a shot if you really hate webmail.

    • TiffanyR's avatar
      TiffanyR
      Moderator
      Hello LPCaillouet,

      I am sorry you are having trouble sending emails with SMTP. If you have not already, I would recommend following the instructions under Contacting Cox for Assistance at www.cox.com/.../email-error-codes.html to see if we can offer any additional insight into getting the IP unblocked to allow sending emails. Please let us know how it goes.

      Tiffany R.
      Cox Support Forum Moderator
      • LPCaillouet's avatar
        LPCaillouet
        New Contributor

        The code I get is CXDNS, as reported in my original post.  That code suggests ..

        “There was an issue with the connecting IP address Domain Name System (DNS).  The Reverse DNS (rDNS) lookup for your IP address is failing.  Confirm the IP address that sends your email.  Check the rDNS of that IP address.  If it passes, then wait 24 hours and try resending your email.”

        This has been going on for several months now, so I needn't "wait 24 hours and try resending".

        Any advice about next steps?

  • LPCaillouet's avatar
    LPCaillouet
    New Contributor

    Really appreciate the help -- and the education!  I'm going to approach Suddenlink/Optimum with my new-found understanding that the modem/router they provided to me is PBL blacklisted and has no DNS Record.  Perhaps that insight will trigger their fixing the problem they created for me.

    (The backstory is that this particular modem/router is a recent replacement by Suddenlink/Optimum of a prior Suddenlink/Optimum-provided device that got fried in an electrical storm a couple of months ago.  With the original modem/router I had no problem accessing Cox SMTP to send e-mail.)

    • WiderMouthOpen's avatar
      WiderMouthOpen
      Esteemed Contributor

      Getting a new IP when swapping out a modem/router combo is pretty normal. Is has a different MAC address so DHCP has to give it a different IP. What isn't normal is must have pulled from a different IP block that doesn't have rDNS/PTR. That is up to Optimum. You might try posting on DSLReports to see if it is possible to fix so your not asking the impossible of their tier 1. Maybe try their direct forum so you can post personal info.

      • LPCaillouet's avatar
        LPCaillouet
        New Contributor

        Thanks for everything!  I have just completed a chat with Suddenlink/Optimum -- they promised a fix in 48-72 hours.  Of course, I've heard that music before...