Newbie Question : EMail servers and MX records

[Julien Matthieu]

i will try to answer you ...


paul williams wrote:
> Hi,
> 
> I'm not too hot on DNS and that kind of thing. My understanding is
> that DNS is a globally connected list which allows host names to map
> to IP addresses.
> 
> How does this work for mail servers using MX entries in the DNS ?
> 
> For instance, we've got a small email server here which processes our
> email for xyz at treysta.net. I understand that theres a DNS entry for
> mail.treysta.net somewhere which points to our mail server.
> 
> So, if someone, say xyz at abc.com sends a mail to me at treysta.net, how
> does it all work. Does it search the DNS for an MX entry for
> treysta.net and then direct it to our mail servers IP address ?
exactly

> 
> Whys it called mail.treysta.net ? Or could it be anything.treysta.net
> just needs to be an MX entry ?
just need to be an mx record

> 
> What happens if email sent is unable to connect to the IP address
> pointed at mail.treysta.net ? Does email get bounced ?
> 
no, most if not all mail transport agent (servers) have timers to
re-try sending the email for a couple of days... so if it can't reach 
the mail server
after x times for let's say 2 days .... it comes back to the sender 
saying the mail server couldn't been reach...


finaly: i'll give you an example of this without the mail in mail.host.org

if you have any question ask ....


; <<>> DiG 8.3 <<>> microsoft.com mx
;; res options: init recurs defnam dnsrch
;; got answer:
;; ->>HEADER<<- opcode: QUERY, status: NOERROR, id: 2
;; flags: qr aa rd ra; QUERY: 1, ANSWER: 3, AUTHORITY: 0, ADDITIONAL: 6
;; QUERY SECTION:
;;      microsoft.com, type = MX, class = IN

;; ANSWER SECTION:
microsoft.com.          2H IN MX        10 maila.microsoft.com.
microsoft.com.          2H IN MX        10 mailb.microsoft.com.
microsoft.com.          2H IN MX        10 mailc.microsoft.com.

;; ADDITIONAL SECTION:
maila.microsoft.com.    2H IN A         131.107.3.124
maila.microsoft.com.    2H IN A         131.107.3.125
mailb.microsoft.com.    2H IN A         131.107.3.123
mailb.microsoft.com.    2H IN A         131.107.3.122
mailc.microsoft.com.    2H IN A         131.107.3.126
mailc.microsoft.com.    2H IN A         131.107.3.121

;; Total query time: 86 msec
;; FROM: sype.org to SERVER: default -- 192.168.1.100
;; WHEN: Fri Jan 10 18:37:51 2003
;; MSG SIZE  sent: 31  rcvd: 193