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1

IN RFC 1025 MX records only point to a RR (resource record) of an A Record or a CNAME. So the mail server sending the mail asks for the RR of an MX record, the mx record lists A records of servers, the mail server does a forward lookup to get an A record and then forwards the mail via smtp to the service host listed as a mail server 'willing' to receive ...


4

I'll throw this out as a guess. Course, I'm home with the flu so maybe I'm loopy. RFC 974 states: The first step for the mailer at LOCAL is to issue a query for MX RRs for REMOTE. It is strongly urged that this step be taken every time a mailer attempts to send the message. The hope is that changes in the domain database will rapidly ...


53

The whole idea behind the MX record is to specify a host or hosts which can accept mail for a domain. As specified in RFC 1035, the MX record contains a domain name. It must therefore point to a host which itself can be resolved in the DNS. An IP address could not be used as it would be interpreted as an unqualified domain name, which cannot be resolved. ...


8

DNS as a protocol has some different types of values, these are not interchangable. It's important to note that DNS is a binary protocol with strict mappings between the type of record and the type of data that such a record holds. For example: An A record holds an IPv4 address (4 bytes of data, fixed length). An AAAArecord holds an IPv6 address (16 bytes ...


2

Some email servers (like exim) specifically do not allow sending to MX records that point to a pure IP address, so you're required to use a FQDN for it instead to be compliant. This is because most servers expect the MX record to contain a hostname, not an IP (that's what A records are for). Edit: To elaborate, in DNS each record has strict requirements for ...


2

Don't. You could configure the guest to use a manually set IP address, but you can't be sure that it will work for every user, nor even for any of them. You can't predict what sort of network environment your appliance will be used in. It's even likely that most people who use your appliance won't use VirtualBox at all, since it's only suitable for ...



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