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Re: RBK50 DNS errors when sending to SMTP server

RBK50 DNS errors when sending to SMTP server

Latest firmware 2.7.4.24. When sending from Outlook or iOS clients, cannot send, error AUP-CXDNS. Shutting off wireless circumvents the issue. Any DNS setting in the ORBI that might correct this? Thanks.

Message 1 of 12
CrimpOn
Guru

Re: RBK50 DNS errors when sending to SMTP server

Google search turned up a number of hits, mostly involving Cox Cable.

Such as: https://forums.cox.com/forum_home/internet_forum/f/internet-forum/29627/cxdns-error-when-sending-mai... 

I love my Orbi.
Message 2 of 12
ekhalil
Master

Re: RBK50 DNS errors when sending to SMTP server

What DNS settings do you currently have in Orbi? Please check this in the Orbi web GUI (orbilogin.com) under >> ADVANCED >> Setup >> Internet Setup >>

My Setup Internet Fiber ONT 250↓/250↑ISP Telenor | Wifi Router Orbi RBR850 + RBS850 + 2x RBS750 + 3xRBS350, Wired/Wireless BH / Orbi RBR50 + 6x RBS50 + RBS40V + RBS50Y, Wired/Wireless BH | Switches NG GS208Time Zone CET (Sweden)

Message 3 of 12

Re: RBK50 DNS errors when sending to SMTP server

My ISP is in fact Cox, but the fact that sending email works normally when not connected to WiFi makes it hard (not impossible) to blame them.

Message 4 of 12

Re: RBK50 DNS errors when sending to SMTP server

Have not changed from the defaults, so:

No Logon required

IP address assignment and DNS settings coming automatically from ISP, two DNS servers provided by my ISP

Default Router MAC address

No DHCP options

No VLAN ID specifications

No Dynamic DNS settings

 

I will add that errors occur whether connected via ethernet or WiFi.  

Message 5 of 12
ekhalil
Master

Re: RBK50 DNS errors when sending to SMTP server

For a test, please try to select “Use These DNS Servers” and set the dns servers to primary 1.1.1.1 and secondary 8.8.8.8 then click on Apply

My Setup Internet Fiber ONT 250↓/250↑ISP Telenor | Wifi Router Orbi RBR850 + RBS850 + 2x RBS750 + 3xRBS350, Wired/Wireless BH / Orbi RBR50 + 6x RBS50 + RBS40V + RBS50Y, Wired/Wireless BH | Switches NG GS208Time Zone CET (Sweden)

Message 6 of 12

Re: RBK50 DNS errors when sending to SMTP server

Will do, though since that would impact the household working from home, it will be (much) later today.  Thanks.

Message 7 of 12

Re: RBK50 DNS errors when sending to SMTP server

Same failures when using the alternative DNS servers suggested.  Now pursuing this as an issue with my ISP, which at the moment is a different ISP than my email provider.

Thanks for the help, and I'll share more later whether fixed or not. 

Message 8 of 12
CrimpOn
Guru

Re: RBK50 DNS errors when sending to SMTP server

Perhaps I read the conversation incorrectly.  It appears that post #4

"email works normally when not connected to WiFi makes it hard (not impossible) to blame them"

 

is inconsistent with post #5

I will add that errors occur whether connected via ethernet or WiFi.

 

I found one comment that this condition was remedied by the ISP creating a PTR (whatever the heck THAT is)

(see post #2 on this conversation: https://www.reddit.com/r/CoxCommunications/comments/vs759s/smtp_outbound_server_from_outlook_when_no...

 

The sense that I get when looking up CXDNS under Cox on this website: https://mxtoolbox.com/Bouncebacks is that Cox is attempting to perform a Reverse DNS Lookup on the IP address that is attempting to connect to the SMTP server and not finding a PTR record.

When I input my public IP address into this DNS Reverse Lookup Site, this is what it shows:

cpe-xxx-xxx-112-236.socal.res.rr.com

What happens when you enter your public IP address into the tool?

https://mxtoolbox.com/ReverseLookup.aspx 

 

 

I love my Orbi.
Message 9 of 12
ekhalil
Master

Re: RBK50 DNS errors when sending to SMTP server


@CrimpOn wrote:

Perhaps I read the conversation incorrectly.  It appears that post #4

"email works normally when not connected to WiFi makes it hard (not impossible) to blame them"

 

is inconsistent with post #5

I will add that errors occur whether connected via ethernet or WiFi.

..............


What I understood is that email did not work when device was connected to home network but it worked when connected to other networks e.g. the mobile network.

My Setup Internet Fiber ONT 250↓/250↑ISP Telenor | Wifi Router Orbi RBR850 + RBS850 + 2x RBS750 + 3xRBS350, Wired/Wireless BH / Orbi RBR50 + 6x RBS50 + RBS40V + RBS50Y, Wired/Wireless BH | Switches NG GS208Time Zone CET (Sweden)

Message 10 of 12
ekhalil
Master

Re: RBK50 DNS errors when sending to SMTP server


@SteveHansen26 wrote:

Same failures when using the alternative DNS servers suggested.  Now pursuing this as an issue with my ISP, which at the moment is a different ISP than my email provider.

Thanks for the help, and I'll share more later whether fixed or not. 


Yes, I think the issue seems between your email provider and the home internet provider. Your email provider is doing an extra security check to validate that email is not coming from dial-up users or a dynamic IP space, which are methods used by spammers.

During a rDNS lookup, your SMTP server (provided by your email provider) verifies that your IP address matches the domain name submitted by the SMTP client in the HELO command. For some reason this is not being passed forward by the internet provider.

As a workaround, I think you can configure another SMTP server (hotmail, Gmail, .....) on your email client.

My Setup Internet Fiber ONT 250↓/250↑ISP Telenor | Wifi Router Orbi RBR850 + RBS850 + 2x RBS750 + 3xRBS350, Wired/Wireless BH / Orbi RBR50 + 6x RBS50 + RBS40V + RBS50Y, Wired/Wireless BH | Switches NG GS208Time Zone CET (Sweden)

Message 11 of 12

Re: RBK50 DNS errors when sending to SMTP server

Ekhalil, you have it right, I believe, in both of your recent posts. Had the opportunity to test from Cox ISP with RBR50, and email is sent without issue. Seems clear that issue is with ISP from my original report and testing. Thanks again, all.

Message 12 of 12
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