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I'm setting up my own mail server for my domain. For example I own "example.com", and I want my server to process all the mail for "example.com".
I keep seeing domain names like "smtp.example.com", "pop3.example.com" and "mail.example.com" - do I have to create those kind of subdomains for this to work? And if so, which ones do I need?
Well, there's nothing special about "smtp." or "mail." - they're just names.
But you might want to consider using something like them. They can make certain future changes a little easier.
All the email clients really need to know is how to get to your mail server. That means as long as they're given a name that somehow resolves to the IP address of the correct server, they'll work. You can even skip that and use the raw IP address when configuring a mail client, and it'll still work. (In fact I know of some people who use the IP address on purpose, simply to avoid the extra look-up time when a domain name is converted to an IP address.)
So any domain name you choose that maps to the IP address of your mail server is a fine choice.
Let's say some day in the future, you want to move your mail processing to a different server. Perhaps you want to offload the server handling "example.com" web traffic, because the email load is getting too high. It's a common scenario, actually, as mail servers are working extra hard these days filtering spam.
If you have a separate subdomain - say "mail.example.com" - that you use for all of your mail configuration, then after you set up your new mail server, all you need to do is change the IP address that "mail.example.com" points to. As DNS propagates, all of your mail processing will automatically move to the new server. No email clients need to be reconfigured.
Now, there's still an issue with DNS propagation that could potentially cause some mail to be delivered on the old server after the recipients have switched to the new - but a separate subdomain solves that problem as well.
The "MX" DNS record tells mailers where to send mail destined for your domain. So perhaps we'd set up a domain "mx.example.com", and use that ONLY for the MX settings for your domain (or domains). We'd still also set up "mail.example.com" for your recipient's client programs to send and receive through. Both would initially point to the same IP address of the same mail server.
Moving mail servers would now be a two step process once the new server was configured. Change "mx.example.com" to point to the new server. Now, wait two days for DNS propagation (or, if you like, monitor the old server and wait until it stops getting mail), and change "mail.example.com". As that propagates, your mail clients will start downloading mail from the new server, including any that may have been queued up from the day you changed "mx.example.com".
But back to the original question: in all these cases I've used subdomains like "mail" and "mx", but in reality they could be anything. "fred.example.com", "example.example.com", "kwijibo.example.com" are all valid names for mail servers. Using more meaningful names, however helps keep things somewhat more understandable.
And for that matter, if you don't foresee the need for flexibility in the future, then "example.com", without a subdomain, is just fine too.
(Just remember to replace "example.com" with your domain, ok?)
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