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I am following this guide on how to set up a mail server, Postfix, and one of the assumptions is that I should have an MX record for mail.mydomain.com. Postfix Guide However, I only have an MX record for mydomain.com, and when I try to DiG it, nothing appears.

I have set up everything, and it works, but it is a little bit alarming, I can telnet into localhost 25 and send an email from anybody with the command mail from: anybody@anywhere.com, and it gets sent without incident. It also displays the recipients as undisclosed recipients.

Do I need to somehow get an MX record for mail.mydomain.com? If so, how do I do that?

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The second paragraph is completely unrelated. It is also expected behavior; this is called an "open relay". Normally you'd require some kind of authentication for any external access, and possibly internal access. Most properly configured mail servers will mark your fake emails as spam, since they see that you're not the domain of the sender and you have nothing showing legitimacy. – Michael Lowman Feb 5 at 18:50
Thanks, having never set up an email server, I was just posting behavior I wasn't expecting. – Cayetano Gonçalves Feb 5 at 19:02
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You usually want to receive mail for address@mydomain.com, not for address@mail.mydomain.com, so an MX entry for mydomain.com will be sufficient, which usually should point to mail.mydomain.com to enable your mail server as an MX.

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Thank you, that clears up quite a bit of confusion then! – Cayetano Gonçalves Feb 5 at 19:05
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