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Old 06-17-2005, 04:22 AM   #1
Registered: Sep 2004
Location: India
Distribution: Solaris 9, FreeBSD 4.10, Slackware, RedHat, Knoppix,
Posts: 84

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Question MX record concept

Hi all,

This is not a problem with linux or any specific OS. I am lacking in concept with MX records. Well i would just like to know why an MX record is needed when i mail someone specifying the exact fully qualified domain name.
When i mail someone to a particular domain, lets say "", in that case, the resolver checks the MX record of and sends the mail to the particular users account using yahoo's inbound mail server. I understand the MX record for is required here to let the resolver know about the mail server(s).
now if i mail some one to a particular host (lets say "") does the resolver again check for the MX records for What i want to know is
does the particular computer has to be an "MX record specified" mail server in order to receive mails from other domains even if it is running a mail server (like sendmail or qmail) ?
Please let me know about this a i m trying to figure out the answer for the last couple of hours (maybe i didnt search well in google).

Thanks in advance,
Old 06-17-2005, 06:25 AM   #2
Registered: Jun 2005
Location: Canada
Distribution: Debian Etch/Sid, Ubuntu
Posts: 529

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No, if you look at, you will se the following MX A
no need for another MX record.

Also, you can send mail to any host with an A record (or ip)
Old 06-17-2005, 06:55 AM   #3
Registered: Sep 2004
Location: Texas, USA
Distribution: Fedora
Posts: 620

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I don't really know if the mail related RFC's specify a delivery order (like MX, then FQDN) for MTA's, but I have noticed that if an MX record is missing, the MTA will try to delvier to the FQDN. i.e.

Note: Just because you can specify a FQDN for the recipient e-mail address, the remote host must also be running an MTA (like postfix) to accept e-mail connections. Furthermore, the remote MTA must be configured to accept e-mail addressed to the FQDN versus the domain name. Most properly configured MTA's will reject e-mail addressed to the FQDN.

Example: MX record points to

E-mail addressed to is accepted, but e-mail addressed to would be rejected. Why? Using postfix for example, the "mydestination" parameter does not allow e-mail addressed to the FQDN to be accepted. i.e. from the postfix file...
mydestination = localhost.$mydomain, localhost, $mydomain
but... if I configured the "mydestination" parameter to include the FQDN (myhostname), then e-mail addressed to the FQDN would also be accepted. i.e.
mydestination = $myhostname, localhost.$mydomain, localhost, $mydomain
Old 06-17-2005, 07:57 AM   #4
Registered: Sep 2004
Location: India
Distribution: Solaris 9, FreeBSD 4.10, Slackware, RedHat, Knoppix,
Posts: 84

Original Poster
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thanks for the replies
i ll tell you exactly what happened....
i have access to a subdomain for a large site (lets say and my subdomain as
now i had set up qmail on ""
it was able to send mails to gmail and gmail recieved it with
when i replied to the mail (from gmail), first of all the messages bounced back saying "mail cannot be delivered to -SMTP relay access denied" - i know that problem has got to do nothing with MX records
now i had set the MX record of to ,
now when i send mails from gmail to, the error message did not appear and no mail delivery failure message was recieved in the gmails inbox (strange: the SMTP relay access denied problem just disappeared)
but at the server ( the mails were not there - i didnt find any mails in that server and the mails seem to just disappear

any clues?


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