How do I set up a mail server in a mail subdomain?

Question

Please forgive me, I'm pretty new at server admin tasks.

I've just moved servers, away from my 'learning' VPS and am about to set up email on my Debian VPS. It'll the second time I've done this. Ever.

I followed this guide, formerly, but ended up with the mail server sitting at the fqdn level, rather than the .mail subdomain. Apparently the latter is a best practise

Please would somebody tell me how I can achieve this?

Many thanks

EDIT: fixed link

@dmmedia - Thanks - I didn't notice the link was wrong :) – Glenn Apr 20 '21 at 10:01 — Glenn, Apr 20 '21 at 10:01
How the hell do I make it more 'focused'? – Glenn Apr 20 '21 at 16:18 — Glenn, Apr 20 '21 at 16:18

score 0 · Accepted Answer · answered Apr 20 '21 at 10:21

The server name is distinct from the domain part of the mail addresses it accepts email for, these need not even be in the same domain.

Typical small-scale setups would use a server name that is unrelated to its function and a CNAME that maps from a name describing the function to the actual server name, plus a few extra DNS records describing the services.

So you'd end up with

.               IN      MX      10 mail
_sip._udp       IN      SRV     10 1 5060 sip

mail            IN      CNAME   cute
www             IN      CNAME   cute
sip             IN      CNAME   cute

cute            IN      A       1.2.3.4

The mapping from service to host name is historically grown: for mail, a separate record type exists that maps the mail domain name to a set of hosts responsible. For the SIP telephony protocol (and a few others), the generic SRV record fulfills the same role. For web sites, no such lookup exists, and instead people use the convention to include a hostname "www" in the URL.

The CNAMEs then map the services to the actual hosts. This could be omitted and the mapping done directly (except for the "www" case), but it is good style to use a separate host name so you can refer to these in other situations (e.g. ssh mail.my.domain will connect you to the mail server wherever it is).

The actual hosts are then configured normally, whether you give them cute names or functional ones depends on your environment.

For SSL certificates, it makes sense to use the host name that the client uses to address them. For mail servers, that is the name in the MX record, i.e. the certificate would use the name mail.my.domain. The CNAME resolution is invisible to the client.

Thanks for your kindness, I appreciate this a lot – Glenn Apr 20 '21 at 10:31 — Glenn, Apr 20 '21 at 10:31

How do I set up a mail server in a mail subdomain?

1 Answers1

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