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421 Error when sending email IP address is not permitted to send messages

New Poster

421 Error when sending email IP address is not permitted to send messages

Hi, I have 3 email programs (Windows Live Mail, Outlook, and Mail Bird) and just in the last 2 days, none of them can send Outgoing messages (Incoming emails are fine).  I've already talked to support and received no assistance.  Here's the error message.

 

An unknown error has occured.  Server Error 421  Server Response:  421 resomta-po-17v.sys.comcast.net

resomta-po-17v.sys.comcast.net CSI IP 174.106.41.120 is not permitted to send messages.

Please contact support if you feel this is in error.

Server: 'smtp.comcast.net' 

Windows Live Mail Error ID: 0x800CCC67

 

That IP address is NOT any of my devices...not my smartphone or computer...does anyone have an idea what I can do?  Thanks

 

New Poster

Re: 421 Error when sending email IP address is not permitted to send messages

I'm having exactly the same problem.  Just started earlier this week.  None of my sent mails have gone out.  The web portal works fine.  I suspect that the IP address is my router address, and it is being blocked by Comcast for some reason, but the support person I chatted with insisted that it was my email software configuration, not their server, since the webmail works. 

New Poster

Re: 421 Error when sending email IP address is not permitted to send messages

Thank you for confirming that I'm not crazy...I have other computers with the same software configuration that have no problem.  It's only this one IP Address that Comcast is blocking...I'm going to keep calling Tech Support until I get someone with the knowledge of what's going on...if you finally get an answer, please let me know what it was!  Thanks!

 

Oh, you can open up a Command Prompt window and type in    ipconfig    then press the Enter key...that should give you the IP Address of your router...in my case, it's not that IP Address that they're blocking...

New Poster

Re: 421 Error when sending email IP address is not permitted to send messages

Thanks, I did verify that it is my IP address that they are blocking.  I'm going to see if my VPN will let me get around it, but I would like to hear from Comcast why they are doing it.

New Poster

Re: 421 Error when sending email IP address is not permitted to send messages

Oops, the Command Prompt Ipconfig command will only give you your Local IP Address, NOT the Public IP Address which is what Comcast is blocking.  For that, go to:

 

https://www.whatismyip.com/

and you'll get your Public IP Address.  That IP Address will match what Comcast is blocking.

Connection Expert

Re: 421 Error when sending email IP address is not permitted to send messages


@Mikeprofla1 wrote:

 

Oh, you can open up a Command Prompt window and type in    ipconfig    then press the Enter key...that should give you the IP Address of your router...in my case, it's not that IP Address that they're blocking...


FWIW, that output gives the private / non-routable LAN interface IP address that the router's DHCP server is assigning to the particular network clients and not the public / routable WAN IP interface address that the Comcast DHCP is assigning to the router / connection.




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New Poster

Re: 421 Error when sending email IP address is not permitted to send messages

I realized that after I typed it..you used much more eloquent language than I did to explain it better...thanks...I'm 61 years old and don't remember all the technical terms any more!  HA!

New Poster

Re: 421 Error when sending email IP address is not permitted to send messages

I tried to bypass by using VPN software but the SMTP server still sees the non-routable IP. 

The problem still remains, why is my IP address being blocked by Comcast, and how do I get it fixed?

Connection Expert

Re: 421 Error when sending email IP address is not permitted to send messages

 .@

 

Smiley Happy




Community Icon
I am not a Comcast employee, I am a paying customer just like you!
I am an XFINITY Forum Expert and I am here to help. For information on the program click here.
We ask that you post publicly so people with similar questions may benefit from the conversation.
Was your question answered? Mark a Best Answer!solution Icon
Community Icon
I am not a Comcast employee. I am a paying customer just like you!
I am an XFINITY Forum Expert and I am here to help.
We ask that you post publicly so people with similar questions may benefit.
Was your question answered? Mark a Best Answer!solution Icon
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I am not a Comcast employee.

Was your question answered?
Mark an Answer!solution Icon

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