What are MX Records?

I was asked to explain MX records today, here it is for others as well:

MX Records, or Mail eXchange Records, is simply a line of text in a file on a DNS Server on the internet.

What it does however is VERY important. It tells other peoples mail servers where to deliver email they are sending to you.

DNS MX RecordThe first MX record (indicated by a lower number, in this example, 10 mail.domain.com.au) is known as the primary MX record. This is where email servers will try to send email first. If it fails, then it will try subsequent MX records (in this example, 20 mail.domain.com.au).

If your email server is hosted onsite on MS Small Business Server 2003 and you change ISP, you will have a new STATIC IP address assigned. Given that your MX record will be pointing to the old IP address, you won’t be getting any email arrive.

To fix this means editing the MX record to reflect the new IP address. That will involve either lodging a job with your hosting provider, or domain name registrar.

4 thoughts on “What are MX Records?”

  1. Thanx, this is helpful, but which IP should the MX record point to? the mail servers internal address or the clients external router address?

  2. Ken, the MX record should point to the clients external IP address (use http://whatismyip.org/ to find this) – Making sure it is a STATIC IP, not a dynamically assigned IP address.

    The clients external router should then pass any port 25 requests though to the internal IP address of the mail server.

    Hope that helps ;-)
    Ben.

  3. thanks for this,I am havoning ongoing problems with web hosting providers being unable or unwilling to point the mx record to my new fixed IP address

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