Southend Linux User Group

SME Server – Part 4

SME Server – Email & Webmail Part 4

Domains structure and incorporation

This is perhaps the complicated part because it largely depends on the domain service provider you are with, what you want from your hosted domain services and what you actually get.

We that is SoSLUG use a company called Andrews and Arnold we do so because they are small enough to care about their customers and large enough to provide a good mix of facilities and options beyond that of more well known domain suppliers, however they are not cheap reasonable priced I guess but not the cheapest.

Some of the obstacles in your way which we consider when we move to a Internet Service Provider is that of contention ratio and block IP addressing. Now contention ratio for those that don’t know is a term expressed when a number of client computers use the same network at the same time and is given as a ratio. Some of the more well know suppliers provide a 50:1 contention ratio or even in extreme cases 100:1 when expressed this way what is being said is that for each router configured this way, a maximum of 50 clients can be routed through one device to the main network at a time in the case of a 100:1 obviously it would be 100 client computers. Also many ISP may also charge for a block of IP addresses these are a quantity of IP addresses that any client computer can use to connect to the internet. 50:1 is better than 100:1 Andrews and Arnold AAISP.net.uk provide for business clients a 20:1 contention ratio so the lower the better for you not them.

Normally you do not need a block of static IP addresses one is usually sufficient, this being the IP automatically assigned or preconfigured by your internet service provider (ISP) on your router. This changes however when you want to run servers and other services off your own network, automatically assigned addresses are all very well but if you hang a server off the IP address assigned by a service provider, when it changes and it does any domain you have assigned to the previous address will failed to route to the server in your network.

Static IP’s is not the only way this can be done but it is the only way we recommend British Telecom do supply Block of IP’s but you will pay for them and you cannot use the BT router they supply it doesn’t work. Of course it goes without saying we do not recommend BT at all the service is second to none, the worst you can possibly imagine and very expensive, if there is a problem with payment due to holidays you will lose your internet connection. This is not good when you are running server services off a BT line.

Andrews and Arnold are not as expensive as BT and have the advantage of providing a preconfigured router and a nifty web interface to configure your domains you pay a £1 for each domain you have assigned to the interface plus another £1 for DNS setup each month for each domain, so yeah not cheap but well worth the money – highly recommended.

Configuring your domain

Any domain name can have a number of services configured to it we are going to talk about two.

subdomains and MX records

So if you have a domain what do you want with a subdomain, let me first explain what a sub domain and a domain actually is. A domain usually but not always is assigned to a website and or in a around about way email. It is usually the first thing you type in a browser “google.co.uk” for example, this is what we call the domain name whenever you use a domain name it resolves to an IP address this is because for us humans it is a lot easier to remember a name than a series of numbers. When we use this domain a route is found via the numbered pathways through other routers ISP etc until the server with the information you are looking for is located and returned to your display. A sub domain extends the domain name by calling it something slightly different but within the bounds of the orginal domain – so still yours, this can be assigned a very different address at absolutely no cost. Hundreds of new domains can be set up this way – “mail.domain.com” where domain.com is your own purchased domainname.

So, say for example you had a domainname called “fishheaven.co.uk” and a fictitious address of 40.128.197.210 of this you have going to your main website and because you are doing rather well at the moment you want your own email services perhaps due to the ridiculous amount of advertising you need get past every time you look at you mail via google, gmail or yahoo.

However you have already used the domainname for your website and ideally like to use the domainname component for your email address. Well not to worry you can and you can do so without touching a subdomain the draw back is that you have to use another IP address and another server (that statement is not completely true but for the purpose of this article it is.), we do this by using the domains own MX record or “Mail eXchange” record all the domain names have them some are easy to configure some are damn hard some are impossible and must be done by an ISP administrator.

Say your email server is on an address of 54.211.56.28 and this is what you have configured your email server to respond to. You simply locate the record for MX from your ISP and enter the correct value for the IP assigned to your server.

When you do this you can not use fishheaven.co.uk to access the server that has your mail obviously this is in use by your website. So how the dickens are you to access your email, well if your server has been configured to deliver email via a web interface you would use http://54.211.56.28/webmail or if via a secure server which SME Server is https://54.211.56.28/webmail using this you need to download the security certificate to access any mail.

So we are back to numbers again bummer! Well no, not if we use subdomains we have an IP address of 54.211.56.28 if we where to assign this to say “mail.fishheavens.co.uk” we can have the best of both worlds IP and sub and domainname. So when we type https://mail.fishheavens.co.uk into the browser now it will point to the email server at 54.211.56.28. This we do using an A record for the domain mail.fishheavens.co.uk where mail is a sub domain of fishheavens.co.uk.

Thats the complicated bit, it perhaps sounds more complicated than it actually is and if you can’t manage this yourself you can ask your friendly ISP administrator to do if for you or provide you with an example. Next I will talk about the configuration via the web interface for this email server series so keep your eyes pealed for the next in this episode.

Author: Derek Shaw - Page reference: 4606
Last modified: Alan Campion - 2015-02-16