It is currently Tue Sep 16, 2014 7:26 am


All times are UTC - 6 hours




Post new topic Reply to topic  [ 31 posts ]  Go to page 1, 2, 3, 4  Next
Author Message
 Post subject: Reverse DNS FAILED! This is a problem.
PostPosted: Fri Dec 04, 2009 10:59 am 
User avatar

Joined: Wed Dec 31, 2008 11:51 am
Posts: 667
Location: Austin, TX
We wanted to give a bit more insight into the Warning from our SMTP Diagnostic tool about Reverse DNS Failing.

When a sending server makes a connection to the recipient server, the recipient server notes the sending IP address and performs a reverse lookup. This is done by sending a DNS query which returns a Fully Qualified Domain Name ( FQDN) registered for that IP address. If the sending SMTP address matches the domain, then it's much more likely that the message is legitimate and therefore will be passed on to the recipient. If the IP address doesn't match, it's much more likely that the sending address was spoofed and therefore much more likely that it's unwanted and could be considered spam.

A FQDN is associated to an IP with a valid PTR record. You want the domain name portion of the FQDN to match the domain of your email address. (e.g. if your sending addresses follow the convention of name@mydomain.com, your PTR record should contain something like mailserver.mydomain.com). Only the organiztion which controls and owns the IP can set a PTR record. PTR record queries are sent to the owner of the IP address which is the ISP, unlike other DNS queries which are sent to the DNS server of whoever owns the domain. For this reason Setting a PTR record on your own DNS servers is almost useless since no one is asking your servers.

To make any changes to your rDNS, you will need to contact your ISP or if you host your own DNS (rare) you will adjust it yourself. You will not be able to do this in your DNS control panel unless your ISP also hosts your DNS and gives you the functionality to add your own rDNS records.

_________________
Wendy Young
Tier 2 Support Analyst
wendy@mxtoolbox.com

Follow us on Twitter at @MxToolBox, Facebook and read the MxToolBox Blog.


Top
Offline Profile  
 
 Post subject: Re: Reverse DNS FAILED! This is a problem.
PostPosted: Thu Mar 18, 2010 11:47 am 

Joined: Thu Mar 18, 2010 11:29 am
Posts: 0
The parsing tool does not seem able to deal with SMTP banners that are sent in multiple packets.

For example, if I my SMTP banner is

220 mail.example.com ESMTP ExampleMailDaemon

but it is sent in two packets (splitting between the S and T in "ESMTP"), then SuperTool reports:

OK - x.y.z.w resolves to

as the complete line. This generates a follow-up warning as the domain name doesn't match "".

This may not be an obvious bug, as splitting at different places doesn't necessarily break it. However, the SMTP RFC is line-at-a-time, so the tool should be agnostic as to the packet boundaries.


Top
Offline Profile  
 
 Post subject: Re: Reverse DNS FAILED! This is a problem.
PostPosted: Tue Aug 30, 2011 1:19 pm 
User avatar

Joined: Tue Dec 30, 2008 2:51 pm
Posts: 276
Location: Austin, Tx
I would love to work on this bug if you could provide me with the address of a server that always returns it's banner in multiple packets. You can email me offline at peter@mxtoolbox.com.

Thanks

_________________
Peter LeBlond
MxToolBox
Product Development Engineer
peter@mxtoolbox.com


Top
Offline Profile  
 
 Post subject: Re: Reverse DNS FAILED! This is a problem.
PostPosted: Wed Sep 14, 2011 12:53 am 

Joined: Wed Sep 14, 2011 12:50 am
Posts: 0
Hi,
thank you, exactly what I'm looking for!


Top
Offline Profile  
 
 Post subject: Re: Reverse DNS FAILED! This is a problem.
PostPosted: Tue Nov 08, 2011 6:36 pm 

Joined: Tue Nov 08, 2011 5:43 pm
Posts: 0
very useful information.


Top
Offline Profile  
 
 Post subject: Re: Reverse DNS FAILED! This is a problem.
PostPosted: Tue Dec 27, 2011 2:34 am 

Joined: Tue Dec 27, 2011 2:28 am
Posts: 0
I realize that I get the message “Reverse DNS FAILED! This is a problem.” Because there is no reverse DNS for my IP Address, that will point on my mail server’s host name. But what if my mail server sends emails through a smarthost? My ISP’s smarthost. Which is a completely legitimate sender. Will the recipient mail server still consider my email as spam?


Top
Offline Profile  
 
 Post subject: Re: Reverse DNS FAILED! This is a problem.
PostPosted: Tue Dec 27, 2011 8:23 am 
User avatar

Joined: Wed Dec 31, 2008 11:51 am
Posts: 667
Location: Austin, TX
nucleus wrote:
I realize that I get the message “Reverse DNS FAILED! This is a problem.” Because there is no reverse DNS for my IP Address, that will point on my mail server’s host name. But what if my mail server sends emails through a smarthost? My ISP’s smarthost. Which is a completely legitimate sender. Will the recipient mail server still consider my email as spam?


In most cases you will be fine, but some services look past the original sending IP and deep scan the header to verify all IPs. If possible we would highly recommend including rDNS so that your IP checks out as well.

Thanks,
Wendy

_________________
Wendy Young
Tier 2 Support Analyst
wendy@mxtoolbox.com

Follow us on Twitter at @MxToolBox, Facebook and read the MxToolBox Blog.


Top
Offline Profile  
 
 Post subject: Re: Reverse DNS FAILED! This is a problem.
PostPosted: Tue Jan 10, 2012 7:23 pm 

Joined: Tue Jan 10, 2012 7:19 pm
Posts: 0
Having a problem with the parsing tool does not being able to deal with SMTP banners that are sent in multiple packets. any help?


Top
Offline Profile  
 
 Post subject: Re: Reverse DNS FAILED! This is a problem.
PostPosted: Thu May 17, 2012 3:31 pm 

Joined: Thu May 17, 2012 2:55 pm
Posts: 0
I'm managing two MX servers (Exchange 2010). Both are on different ISP's.

MX servers are as follows:
*removed*

When remoting to one of our offsite Linux boxes, I performed the following commands to test rDNS:
*removed*


*removed* I'm just wondering if there's a reason mxtoolbox doesn't pass our rDNS test.

Regards,
Tom


Last edited by twright70 on Mon May 21, 2012 8:15 am, edited 1 time in total.

Top
Offline Profile  
 
 Post subject: Re: Reverse DNS FAILED! This is a problem.
PostPosted: Thu May 17, 2012 3:41 pm 
User avatar

Joined: Wed Dec 31, 2008 11:51 am
Posts: 667
Location: Austin, TX
twright70,

Thanks for your post, it appears that 12.154.216.240 is receiving a warning because the rDNS and SMTP Banner do not match. For more details on this warning, review this blog post.

Let me know if you have any other questions.

Thanks,
Wendy

_________________
Wendy Young
Tier 2 Support Analyst
wendy@mxtoolbox.com

Follow us on Twitter at @MxToolBox, Facebook and read the MxToolBox Blog.


Top
Offline Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 31 posts ]  Moderator: MXToolbox Go to page 1, 2, 3, 4  Next

All times are UTC - 6 hours


Who is online

Users browsing this forum: Yahoo [Bot] and 5 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum

Search for:
Jump to:  
cron
{ ASACP_CREDITS }
Powered by phpBB © 2000, 2002, 2005, 2007 phpBB Group
Theme created StylerBB.net