Visit Jeremy's Blog.
Go Back > Forums > Linux Forums > Linux - Networking
User Name
Linux - Networking This forum is for any issue related to networks or networking.
Routing, network cards, OSI, etc. Anything is fair game.


  Search this Thread
Old 06-23-2004, 10:55 AM   #1
Registered: Jun 2003
Location: West Grove, PA
Distribution: Gentoo, Debian, SuSE, Mandrake
Posts: 55

Rep: Reputation: 15
eMail Blocked due to Reverse DNS Issue

I have a DSL line and purchased a block of addresses so that I can run my own DNS server, web server, mail server, etc. I operate several domains within this IP block, maintaining DNS and reverse DNS entries on my name server.

Lately I have found that some of my out-going eMails are being blocked because when the receiver's mail server does a reverse DNS lookup of my server's IP address, they get a Sprint DSL domain name, not the domain name I have registered. For example, if your run a "dig" command against my domain you can find the MX record of However, if you do a reverse DNS of this same address, you get "".

Many large ISP's use commercial spam filters (such as which will drop any message where the domain name does not match the reverse DNS domain.

I haven't contacted Sprint to try to get their reverse DNS entry removed yet, but suspect that they will be hesitant to remove their entry. And if they do, how can I get the world to look at my server to find the reverse DNS entry?

Any suggestions for how to fix this problem (which will probably only get worse as time goes by) would be very much appreciated.

Casey Bralla
Chief Nerd in Residence
The NerdWorld Organisation
Old 06-23-2004, 11:33 AM   #2
Senior Member
Registered: Jun 2004
Posts: 2,553

Rep: Reputation: 53
i'm not sure but since the ISP owns the IP number
you will need their cooperation and they will have to change
rDNS lookup
hopefully they will do that ??

Last edited by foo_bar_foo; 06-23-2004 at 11:35 AM.
Old 06-23-2004, 03:06 PM   #3
Registered: Feb 2003
Location: Toronto
Distribution: RH8 / FC1 / Gentoo / Debian / FreeBSD / Centos / Ubuntu
Posts: 182

Rep: Reputation: 35
I've been running an email server for about a year and a half. When I first set it up I was having configuration problems and I wondered if this was the issue. I have heard that some large ISPs do this. I have also heard that some simply check to ensure a reverse DNS entry exists, but do not necessarily need it to match your domain.

In my opinion, this approach by large ISPs is stepping on the little guy. Their goal is to prevent spam, but the result is to shut out small legitimate email servers. Having said that, I have not bumped into this as a major problem. In fact, I do not think it has affected me at all at my server.

I have heard that some ISP will accommodate you with reverse DNS. Others will not.
Old 06-23-2004, 03:28 PM   #4
Registered: Aug 2003
Location: Little Rock, Arkansas
Distribution: RH, Fedora, Suse, AIX
Posts: 736

Rep: Reputation: 31
Yeah, this actually did affect me. I had to ask my ISP to setup PTR records (which is techno-speak for reverse DNS) so that the reverse DNS lookup matched the domain of my mail server. For example, if my mail server is, you need your PTR records to say the same thing. This is the absolute best way to have it setup. This way, everything matches perfectly and there should be no problems.
Old 06-23-2004, 04:23 PM   #5
Senior Member
Registered: Jul 2003
Location: Silicon Valley, USA
Distribution: OpenBSD 4.6, OS X 10.6.2, CentOS 4 & 5
Posts: 3,660

Rep: Reputation: 69
Yes, if your ISP will make Reverse DNS (PTR record) changes for you, then that is the best way to do it. Some times your ISP won't do that (too much work for them) or some times stupid companies subscribe to RBLs (Realtime Blackhole Lists) that block any IPs from dynamic assignment blocks, or even any IPs from broadband networks.

In that case, there's not much you can do except call up the company you're trying to send mail to and plead with them to use some common sense and dictch their error-porne methods of blocking spam. RDNS for example has some very fundamental problems, like what happens if one server hosts more than one e-mail domain? That's a perfectly legitimate e-mail setup, but most RDNS implementations will block all the mail that doesn't match the domain from the PTR record.

There are much much more accurate ways to block spam (although most of them cost money). The current generation of commercial anti-spam technology is very good if you purchase from the top vendors (or very poor if you purchase from one of the low-tier "me too" vendors).

If all else fails, ask the administrator of the domain you're sending to for a whitelist entry that will allow your e-mail to bypass their normal filters.


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is Off
HTML code is Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
DNS Blocked by gateway! Samhein Linux - Networking 4 11-28-2005 04:46 AM
No reverse DNS??? DragonM15 Linux - Networking 5 11-22-2005 12:06 AM
email being blocked by spam filters - New postifx setup newtommy Linux - Software 4 05-05-2005 04:03 AM
Reverse DNS issue... WeNdeL Linux - Software 4 09-16-2004 02:35 PM
email blocked by eshield(AVStripper) telemam Linux - Networking 0 04-20-2004 01:43 AM > Forums > Linux Forums > Linux - Networking

All times are GMT -5. The time now is 12:24 AM.

Main Menu
Write for LQ is looking for people interested in writing Editorials, Articles, Reviews, and more. If you'd like to contribute content, let us know.
Main Menu
RSS1  Latest Threads
RSS1  LQ News
Twitter: @linuxquestions
Facebook: linuxquestions Google+: linuxquestions
Open Source Consulting | Domain Registration