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Is mx record means once anyone want to send the mail to others, they have to go to dns to register a one mx record , that is a domain name, such as hotmail .com, in this domain name will point to at least one address of the server.

So , it introduce reverse dns, which is , when I send the mail to the others, the other side will check whether the 'from' ip has a domain name in public dns , if the ip can not find any domain name related to it, the mail server will block the incoming message.

Is my concept correct? And what is A record and PTR do ?

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closed as off topic by womble, EEAA, mailq, voretaq7 Aug 3 '12 at 16:07

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Re: the last line of your question, And what is A record and PTR do ?, I STRONGLY suggest picking up a copy of DNS and BIND -- This question indicates a fundamental lack of understanding re: the concepts underlying DNS, which this book will help remedy. –  voretaq7 Aug 3 '12 at 16:09
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1 Answer

up vote 2 down vote accepted

If I send an e-mail to yourdomain.com, it checks for the MX-records of yourdomain.com to find which mailserver(s) handles this.

Your second paragraph is correct. Many enables the option to check the reverse lookup of the IP sending the e-mail.

Your concept is correct indeed!

A-record is a record pointing to the IP-address of a server. A typical record could look like: yourdomain.com 521 IN A 192.168.1.1 (<- random IP)

When you run a ping against yourdomain.com it will try the IP listed in the A-record.

PTR records are reverse lookup records.

I hope any of this makes sense!

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To add: you are not supposed to send emails froma home server, use a real server / your provider to rlay. Home servers are notoriously ONLY sending spam. Noone accepts email from dynamic address space. –  TomTom Mar 27 '12 at 8:50
    
then what is the difference of mx and a record? –  foodil Mar 27 '12 at 8:53
    
MX is specific for mail-traffic. –  xstnc Mar 27 '12 at 8:54
    
is mx record is for email domain and a record is for webpage? –  foodil Mar 27 '12 at 8:54
    
That's one way of putting it yes! –  xstnc Mar 27 '12 at 8:55
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