[Semibug] DDNS & PTR

Mark Moellering markmoellering at psyberation.com
Fri Apr 19 20:57:09 EDT 2019

I don't have comcast service.  I have golightspeed, which was just 
acquired by MetroNet.  I have fiber to the home and port 25 is open :-)

but I can't email anyone with a comcast address.  Their mail server very 
helpful says:

host mx1.comcast.net[] refused to talk to me: 554 
resimta-po-34v.sys.comcast.net resimta-po-34v.sys.comcast.net Comcast requires that all mail servers must have a PTR 
record with a valid Reverse DNS entry. Currently your mail server does 
not fill that requirement. For more information, refer to: 

There are other networks with similar messages.  Right now, I have my 
domain through Godaddy.  I will have to see if they offer DDNS

Thanks for the reply

-- Mark

On 4/19/19 6:47 PM, Anthony Cascianelli wrote:
> Comcast will sell you a static IP address. But you might be surprised at how seldom your Comcast IP changes. I’ve been in my current house for over 2 years and I’m pretty sure it’s never changed.
> How are you running a mail server on residential Comcast service?  I thought they specifically blocked inbound on those ports.
> Whose late you hosting your domain name through?  I use Namecheap and they offers a DDNS update service.
> Anthony Cascianelli
>> On Apr 19, 2019, at 8:29 PM, Mark Moellering <markmoellering at psyberation.com> wrote:
>> How hard is it to get a PTR record for a dynamic (home) IP?  I am running my own email server and Comcast demands a PTR
>> I think you can do it with DDNS but I am not sure of the best place to set that up.  Any pointers?  Is there any way to buy IP addresses and just have them forward to my home IP. or is that laughably difficult?
>> Thanks, and I hope this makes it to the list
>> -- Mark
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