Configure Exchange E-Mail Server Reverse DNS and MX Records Correctly

If DNS is setup incorrectly, over time your mail server IP will be added to blacklists. Nowadays most E-Mail servers have some kind of spam protection service which in turn means that all your inbound mail will be blocked if you do happen to be listed on a spam blacklist.

In this article I will describe how to correctly configure your MX and reverse DNS records for your mail server. This article is based on an Exchange 2003/2007 server but every other messaging server will follow the same principle.

Assigning an IP address

Starting from the bottom up the first thing you need to do is assign a static external IP address to the internal private address of your mail server. You will need to apply these rules on your firewall to port forward SMTP (port 25) and NAT an external IP address to the internal address of the server.

Something that a lot of administrators forget to do or check is to set the outgoing NAT rule to use the same external IP address created for the inbound rule to the mail server. If this is not set, Reverse DNS will not match and in turn your mail server will be listed on blacklists. If your firewall rules are set up correctly the IP address listed on this page should be the same IP address you mapped to the internal private IP address of the mail server.

Create the MX records for your mail server

For the purpose of this example, listed below are all the details of my mail server to help you understand what you need to do.

External IP:

E-Mail Domain:

You will need to be an administrative contact for your External DNS provider for your domain to make these changes. In most cases this can be done through an online control panel through your DNS provider. Failing that on the phone or via E-Mail.

1. The first thing we need to do is create an A record to point to the external IP address mapped on your firewall to the mail server. The host A record can be called any thing but is commonly called "mail". In our example we will create "" to point to IP address ""

2. Next we will create an MX record to point to the newly created A record of our mail server.

Within your DNS control panel select "add MX record". Make sure that the host address is the root domain name in our case ""

Set the FQDN as the A record we just created which in our case is "".

The lowest property is the most preferred but in our example we will set the priority as 10.

Use NSlookup to check DNS and MX records are applied

It can take up to 48 hours for DNS to propagate but in most cases 12-24 hours. To check our DNS entries are applied and correct we can use nslookup.

1. Open a CMD prompt and type nslookup

2. Type set type = mx

3. Type the domain name which in our case is .

In our example the output should read as follows if correctly setup:


Non-authoritative answer: MX preference = 10, mail exchanger = internet address =

Configure Reverse DNS

Reverse DNS is used to verify that the mail server is who it says it is. The recipients mail server will do a reverse lookup to make sure that the IP address of the mail A or host record in DNS is the same as the IP address it is communicating with. Only 1 RDNS entry can be present per IP address.

To do this you will need to contact your ISP to make this entry. You will not be able to do this in your DNS control panel without your ISP also host your DNS and give you the functionality to add your own RDNS records.

In our case we would contact our ISP and advise that we would like to create an RDNS entry for our IP address which would resolve too .

Verify Reverse DNS

Again it can take up to 48 hours for DNS to propagate but in most cases 12-24 hours. To verify that the RDNS entries have been added and are correct do the following:

1. Open a CMD prompt.

2. Type Ping -a (This is the external IP address for your mail server. In our case we use our external IP address above)

If RDNS is configured correctly the following output will be shown:

C: UsersUser> ping -a

Pinging [] with 32 bytes of data:

SMTP Banner

Every time a mail server establishes a connection with your mail server it shows its SMTP banner. This banner must be resolvable on the internet and best practice is to have it as your mail host / A record.

Configure SMTP banner Exchange 2003

1. Open Exchange system manager .

2. Expand your administrative group ("First administrative group" by default).

3. Expand Servers .

4. Expand YourServerName .

5. Expand Protocals container.

6. Select SMTP container.

7. On the right window, right click the Default SMTP virtual Server (and Or the name you set your SMTP Server) and

select Properties .

8. Select the Delivery Tab.

9. Click the Advanced button.

10. Under the Fully-qualified domain name type (The A / Host record you created in DNS for your mail server)

11. Click OK and OK again to accept the changes

Configure SMTP banner Exchange 2007/2010

1. Open the Exchange management console .

2. Select the Organization Configuration container.

3. Select Hub Transport container.

4. On the right select the Send Connectors tab.

5. Right click your send connector and select properties .

6. On the General tab under the Set the FQDN this connector will … type the A record domain name you created. Which in our case is . Click OK .

7. Under the Server Configuration container click the Hub Transport container.

8. In the Right window Select the properties of the Receive Connector under Receive Connectors tab.

9. On the General tab under the Set the FQDN this connector will … type the A record domain name you created. Which in our case is . Click OK

To verify these changes we can use telnet to view the output upon establishing a connection on port 25 to our mail server. Use the following steps to do this:

1. Open a CMD prompt

2. Type Telnet 25 .

The output you see should look something like this and contain your A record of your mail server:

220 Microsoft ESMTP MAIL Service ready at Sun, 28 Feb 2

010 17:51:20 +0000

If you use an edge server or a SPAM filter appliance like a Barracuda the SMTP banner will have to be set on this device / server.

Check to see if your mail server is on spam lists and / or an an open relay

A great website to use to check your MX records, RDNS, check if your mail server is an open relay and check to see if you are listed on spam lists is . This is a great site and one to keep in your favorites.

Following these guide lines will successfully and correctly configure mail routing to and from your mail server. The next step is too secure and ensure your mail server is not an open relay. I will be writing a separate article dedicated to this in the near future.

Source by Mike S Collins

Reverse Osmosis Water Filters – The Whole Shocking Truth About Reverse Osmosis!

Reverse osmosis water filter has quickly become a buzzword in the bottled industry. It is so popular that many companies producing drinking water employ the byword as a corporate tagline.

Question number one: How much do you really know about reverse osmosis filter?

Question number two: Is it really effective in giving us balance and ideally clean water?

Let us try to evaluate these questions and try to provide you the seemingly elusive answers.

What is reverse osmosis?

Reverse osmosis is a filtration technique where water is forced by extreme pressure to pass through a permeable membrane. First, apparently dirty source water is treated. Later, the still unclean particles is mechanically forced to pass through a membrane where the solvents are trapped by the membrane and the solute, in the form of ultra clean water, passes through.

Technically, there are varying stages required before the product output is certified as fit for human consumption. A sediment filter is initially used to eliminate dissolved solids in the untreated water. A secondary sediment filter may be used to further get rid particles with smaller sizes. Activated carbon filter and ultraviolet lamp are typically used to eradicate organic chemicals, elements and microorganisms.

Reverse osmosis produces completely demineralized water. Many companies call this as pure drinking water. But is this the ideal drinking water we really aspire and need?

The answer is no.

Our body has been designed to take in trace elements naturally found in normal drinking sources. Drinking water must be able to retain the calcium, magnesium and phosphorus elements naturally dissolved in our drinking water. Unfortunately, reverse osmosis water filter is so effective that it completely gets rid of everything in the water. It produces thoroughly demineralized water. What are the risks involved with this technique?

Why reverse osmosis does not serve its purpose in providing us quality and safe water?

Continued consumption of demineralized drinking water will lead lead to mineral deficiencies. Reverse osmosis water filter deprives us of the many elements nature has intended us to acquire from drinking water. Likewise, water produced using reverse osmosis has a much higher acid level, with ph level typically reaching below seven. This is because the water output contains more hydrogen.

Having realized that, the next move now is to find the right kind of water filter that answers not just this issue but all other issues confronting any practical and wise consumer like you.

When buying a water filter, consider its optimal performance. You can find this in the Performance Data Sheet. It tells you what specific contaminants it is certified to remove. It also informs you the extent these contaminants are actually removed. This also explains why water filters are far better than bottled water type since the latter is not highly regulated. In fact, the US Food and Drugs Administration only requires that bottled water should be of the same quality as your tap water.

You also need to consider the price, installation costs, convenience to operate and maintenance.

Every one needs to have easy and convenient access to a water filtering system that delivers the highest performance rating. We should all strive to acquire that. Meantime, you better stop utilizing reverse osmosis water filter.

Source by Zach Smith