What is IP Binding for Domain Groups and how to use it?

You can use IP binding for domain groups if your computer has more than one IP address, and it listens on all of them (value of Options - Server Options - IP Binding - Listen on the Following IP Addresses is All Available).

Use of IP Binding for domain groups makes your server behave as if each domain group was completely independent from each other, like each domain group was running its own virtual server, with its own SMTP greeting, SMTP EHLO/HELO fully qualified domain name, and it's own bounce-from email address.

Let's assume you have two IP addresses on your computer, 111.111.111.111 and 222.222.222.222, also, you want to serve two domains, which are not related to each other (under "not related" we mean, that they do not need to share users, they are not in the same domain group, they are not aliased to each other):  one.com and two.com.  You have created two domain groups on your server: Domain Group One, with the domain name one.com, and Domain Group Two, with the domain name two.com.

Let's consider the case when we are not using IP Binding for Domain Groups (Edit Domain Group box we will see if we select a domain group, and click Edit button on the Domains and Users page, the settings of Bind To field is either Any Available, or the IP Binding box is completely disabled - it will happen if a Listen on the Following IP Addresses box on the Server Options box is anything but All Available).  Let's assume, the setting of the Local Host box on the Options - Server Options - General box is mail.one.com, and the value of SMTP Greeting is blank (empty).

Try to telnet to the port 25 of your server, using all possible IP addresses, go to the DOS prompt, and type:

telnet 111.111.111.111 25

and, later:

telnet 222.222.222.222 25

We will see the similar greeting from the server, which will look like:

220 mail.one.com ArGoSoft Mail Server SMTP Module v.1.0.4.9 at Sun, 25 May 2008 01:04:05 GMT

Pay attention to the mail.one.com.  This is the value comes from Server Options - General box, where it is specified as Local Host.

Now, let's enable IP Binding for domain groups.  Let's select Domain Group One, on the Domains and Users page, click Edit, and in the Bind To box select 111.111.111.111, in the Local Host box type mail.one.com, leave Bounces From and SMTP Greeting boxes blank for now.  If they are blank, then values will be taken from general settings, either from Server Options, or Services...

Do the same with the Domain Group Two, select 222.222.222.222 in the Bind To box, and type mail.two.com in the Local Host box.

Now, we can see results. Telnet to 111.111.111.111, port 25. Greeting will look exactly the same:

220 mail.one.com ArGoSoft Mail Server SMTP Module v.1.0.4.9 at Sun, 25 May 2008 01:04:05 GMT

But, if we telnet to 222.222.222.222, that's what we will see:

220 mail.two.com ArGoSoft Mail Server SMTP Module v.1.0.4.9 at Sun, 25 May 2008 01:04:05 GMT

This time, mail.one.com and mail.two.com came from Edit Domain Group boxes.  For the first domain we see the same value (mail.one.com), because that's what we have entered in the Local Host box, and for the second domain we see mail.two.com, from the similar location!

That's IP Binding for domain groups in action, and it does not stop just here. If you specify SMTP greeting for each domain, they will be selected according the the connecting IP address, and (it is important) if we go back to Options - Server Options - IP Binding box, and select Same as Incoming in the For Outgoing Mail... box, then the server will use mail.two.com with SMTP EHLO/HELO command when delivering to exchangers, if the message being relayed was sent via 222.222.222.222, and mail.one.com, if mail was received at 111.111.111.111.  It means, it will identify itself as a server, serving the particular domain.

Usually, it is not required that the server identifies itself as one from some particular domain, but, if it does, it adds your emails more credibility. It also may be important for owners of domains you are hosting on your server to see the name of their server in SMTP greetings.

Starting from v1.0.5.0, you can enable SMTP connections to specific IP addresses from the Web Intrface, and take advantage of the IP binding feature of the mail server.

Starting from v1.0.5.0 web interface uses remoting services to communicate with the mail server. For sending mail out, it uses SMTP protocol.  You can associate domain names of logged in users with specific addresses of SMTP servers, which will be used for sending mail out when logged in user has a matching domain in his/her user name.

This document describes how to associate domain names with SMTP servers when using web interface.


If you have further questions, please submit it from our Support Page.

Back to the list of documents

Back to the Mail Server .NET FAQ

Back to the Mail Server .NET