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What is a MX Record?

By jim ·
I have a client who wants us to produce their email's MX record so that they can forward some message to someone. My problem is that I don't know what a MX record is. Any help?

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What is a MX Record?

by cberardino In reply to What is a MX Record?

Domain Name System (DNS) entries for Mail Exchanger (MX) records should point to canonicalized host names. MX records should address fully- qualified principal names or domain literals. Pointing an MX record to an alias (CNAME) can cause misrouted inbound mail.

DNS is used to identify computers on the Internet. The Internet Mail Connector (IMC) uses DNS to resolve IP addresses when sending mail. A sending SMTP server also uses DNS to determine which host on the destination network is appropriate to receive mail. To determine mail hosts, the sending server checks for an MX record. Next, the sending server resolves the MX record to an IP address by checking for an address record (A record). If an A record is found, the address is fully canonicalized and mail can be delivered.

However, if an alias record (CNAME) is used for the hostname listed in the MX record, the sending host might re-write the envelope and redirect the RCPT command to the alias hostname and not the original recipient. This might cause the destination SMTP host to reject the message.

Example:


company.com. MX 10 mail.company.com.
mail.company.com. IN CNAME server.company.com.

When you address mail to "admin@company.com" with the above configuration, the sending host might detect the fact that the "mail.company.com" is an alias and rewrite the RCPT-TO command to "server.company.com". Thus, the mail envelope written during SMTP mail transmission might be changed to "admin@server.company.com". If the mail system isn't configured to accept mail for "server.company.com" the message will be returned as undeliverable. This problem can be difficult to detect since the body of the message with the TO: line is left unchanged.

Desired Configuration:

company.com. MX 10 mail.company.com.
mail.company.com. IN A 127.127.127.127

In the above example, the MX record resolves direc

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What is a MX Record?

by jim In reply to What is a MX Record?

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What is a MX Record?

by jim In reply to What is a MX Record?

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