mjhjmtu

I'm configuring DNS server in linux and cannot understand these things. There is no information in the Internet about them:

1. 
   

   Must A record be same as PC name? For example, my PC's name is PC1 and in my PC there is a mail server configured with domain example.com.
   
   
   Should my friend (at his office) write in his DNS zone file(zone file for my domain at his office in his linux server) A record like this:

   
   
   

   PC1 IN A 192.168.1.125

   
   
   

   IN MX PC1.example.com.
   
   
   
   Am I right? Or can we put any convenient for us name for A record?
   
   
   

   
   



2. Must I create seperate zone files for each domain for sending mails to them from my domain?

Local hostname and DNS names is a different things. You can type any hostnames at your server (or PC; not matter) and any public DNS names.

But! Some operating systems (Windows especially) can deny access to himself if you try to connect with different names (names that differ from server's hostname). But it is not your case.

There are some things about mail servers:

1. 
   

   Is a good practic that your hostname return real MX name with command hostname -f

   
   
   

   Example: hostname -f on server return mail.example.com; MX record for domain example.com point to mail.example.com

   
   


2. 
   

   Mail server may (and must in most cases) return HELO with valid DNS record:

   
   
   

   open example.com 25
   Trying 12.34.56.78...
   Connected to example.com.
   Escape character is '^]'.
   220 mail.example.com ESMTP Postfix
   

   
   



3. IP address of mail server must have any ptr record (for good spam reputation) and may have ptr record that resolv to MX record (some "improperly" configured mail servers required strictly accordance of MX --> A --> IP --> PTR (like A record). For example domain: example.com MX --> mail.example.com --> 12.34.56.78 --> mail.example.com).

No, the hostname of the machine does not need to be available in DNS.

BUT ... the machine must be able to look itself up. So it is always best to put the local hostname in /etc/hosts (or equivalent) pointing to a loopback address.

Should that same hostname be a fully qualified domain name, and be in DNS, and pointing to the IP the machine has, well that is OK too. But it isn't required.

FWIW I've just checked my 2 desktops, my Raspberry Pi, and my Linode machines and NONE of the hostnames are in DNS - they are in each machine's /etc/hosts though, all pointing to 127.0.1.1 or 127.0.0.1