RDNS_DYNAMIC 2.60 Delivered to internal network by host with dynamic-looking rDNS

keat63

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Nov 20, 2014
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I'm in the process of migrating from one server to another.
Part of my testing phase was to send a few test emails from one domian to another (between the two different servers)
When sending from the new server to the old one I see the following Spam score (on the old server).

RDNS_DYNAMIC 2.60 Delivered to internal network by host with dynamic-looking rDNS

I enabled 'Sender Rewriting Scheme (SRS) Support' in Exim config and the errors went away.

I'd just like to know the implications of this setting and any thoughts on what's causing it.
Bearing in mind that I've not yet fully migrated all the accounts over, could it be related to this ??
 

cPanelLauren

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Nov 14, 2017
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Hi @keat63


The full definition of RDNS_DYNAMIC is as follows:

RDNS_DYNAMIC indicates that the Reverse DNS check on that IP address resolves to something that resembles the FQDN of a dynamically issued IP address.

Sometimes this is an invalid PTR record as well.

I'm not sure how this relates to enabling SRS Support though as that's specific to forwarding mail:
This option rewrites sender addresses so that the email appears to come from the forwarding mail server. This allows forwarded email to pass an SPF check on the receiving server.

ALL SRS Support does is allow an SPF check to complete successfully on forwarded mail. It rewrites the sender to look like it's originating from the server that performed the forward.
 

keat63

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Considering that its a new server commission, I wonder if rDNS had not quite finished propogating or something??

Now about 36 hours in, I just disabled the setting and sent another test email and now i no longer see that error.

Too much of a coincidence that the error went away immediately after setting 'Sender Rewriting Scheme (SRS) Support' though.
 
Last edited:

keat63

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My server came out of the box with a host name something along the lines of:

123.45.67.89.srvlist_my_host.co.uk, would this qualify as a FQDN of a dynamically issued IP address
However I'd changed this maybe a good 12-24 hours previous to me finding the spam score.