Apple Mac OS X Server Version 10.4 or Later Manual do Utilizador descarregar pdf (Página 20)

20 Chapter 1 Mail Service Setup

Using Network Services With Mail Service

Mail service makes use of network services to ensure delivery of email. Before sending

an email, your mail service will probably have a Domain Name System (DNS) service

determine the Internet Protocol (IP) address of the destination. The DNS service is

necessary because people typically address their outgoing mail by using a domain

name, such as example.com, rather than an IP address, such as 198.162.12.12. To send an

outgoing message, your mail service must know the IP address of the destination. The

mail service relies on a DNS service to look up domain names and determine the

corresponding IP addresses. The DNS service may be provided by your Internet Service

Provider (ISP) or by Mac OS X Server, as explained in the network services

administration guide.

Additionally, a mail exchange (MX) record can provide redundancy by listing an

alternate mail host for a domain. If the primary mail host isn’t available, the mail can be

sent to the alternate mail host. In fact, an MX record can list several mail hosts, each

with a priority number. If the lowest priority host is busy, mail can be sent to the host

with the next lowest priority, and so on.

Mail services use DNS like this:

1 The sending server looks at the email recipient’s domain name (it’s what comes after

after the @ in the To address).

2 The sending server looks up the MX record for that domain name to find the receiving

server.

3 If found, the message is sent to the receiving server.

4 If the lookup fails to find an MX record for the domain name, the sending server often

assumes that the receiving server has the same name as the domain name. In this case,

the sending server does an Address (A) lookup on that domain name, and attempts to

send the file there.

Without a properly configured MX record in the DNS, mail may not reach your

intended server.

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Apple Mac OS X Server Version 10.4 or Later Manual do Utilizador Página 20