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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?
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WiderMouthOpen
Esteemed Contributor III
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3.5K Messages
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.
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Darkatt
Honored Contributor
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2K Messages
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.
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LPCaillouet
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9 Messages
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?
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LPCaillouet
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9 Messages
Looks like "Spamhaus ZEN".
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LPCaillouet
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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?
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LPCaillouet
New Contributor
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9 Messages
I checked PTR for my IP address and got "DNS not found".
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LPCaillouet
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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.)
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