You’ll notice that sometimes you may see two or more MX records – why? If the fist server is unavailable or busy, the sending host will know to try the second server before backing off and retrying. Often the secondary MX record will point to a mail spooler at the companies ISP. This often guarantees a measure of mail delivery and buys additional time to accept mail, as opposed to being marked as “busy”.

The other this you’ll notice is that there are several records with the same OR different MX preferences. That’s easily explained, MX records with low preferences get tried first, then the next higher, and so on, until you run out of MX records.

What about smart hosts? A smart host is another mail server that accepts inbound SMTP and routes it out again – however the point of sending your mail to one of these is that you may offload the task of routing and retrying mail to another location. It makes a lot of sense to point to a SMTP host at your ISP that is configured accordingly, which means your outgoing internet connection frees up much quicker than before. Other reasons may include outsourcing some of your mail/spam/AV to another company.

Why should you care about knowing any of this? Well if you don’t and have been tasked to setup mail for a new organization, where do you start?

Here’s the quick 5 step guide to setting up mail for an organization – without going into o much detail

1. Get an internet connection with a Static IP address(es) –at least one IP is necessary
2. Register your company’s domain, e.g. xyz.com
3. Register an A record to point to one of your static IP’s e.g. mail.xyz.com
4. Register at least one MX record to point to the A record you registered on your previous step
5. Configure your firewall – you do have one of these right? –to accept inbound traffic for the IP address we mentioned in the 2, and route it into to your mail server, that should be configured to be listening for mail for your domain

Connect to the internet -outside of your network and test the connection – how do you do that? Have a look at a previous article I wrote, that may be found here.