What is a Mail eXchanger (MX) Record?
MX records control how e-mail is delivered. They are used to locate the receiving mail servers for a given host, and the order of priority of these mail servers. Here is an example of an MX record:Host TTL Type Data example.com 43200 MX 10 mail.example.comAn MX record is composed of four parts:
- The Host field indicates the email addresses that the MX record handles (in this case, @example.com).
- The TTL (Time To Live) field indicates the length of time in seconds that this record should be cached.
- The Type field indicates the type of record (such as A, CNAME, MX, PTR, etc.).
- The Data field consists of the MX record's Preference and the destination mail server.
Do I need MX records for my domain?
Technically, a domain does not require MX records to receive email. By default, a sending mail server should attempt to deliver mail to the host itself if no MX record is present. For example, if a sending server is trying to deliver mail to user@domain.com, and domain.com has no MX records, it will try connecting to any mail server at domain.com itself.However, it is highly recommended to create MX records for your domain, even if they seem redundant or unnecessary; in the above example, domain.com should still have at least one MX record set to domain.com itself to help ensure delivery, like so:
domain.com 43200 MX 10 domain.comSome non-RFC-compliant servers will fail to deliver email for domains that lack MX records, including certain versions of Microsoft Exchange, and there is certainly no harm in creating redundant MX records for your domain. (Naturally, if you do not have a mail server for your domain at all, MX records are unnecessary.)
What does the Preference value mean?
An MX record's Preference value determines its order of priority, with 0 being highest/first priority and 50 being lowest/last priority. If the highest priority mail server is unavailable for any reason (time out, power outage, etc.), sending mail servers try to connect to the next-highest mail server; if this mail server is also unavailable, it goes to the next-highest, and so on down the list.Here is an example of a domain with two MX records:
example.com 43200 MX 10 mail.example.com example.com 43200 MX 20 backup.example.commail.example.com has a Preference of 10 and backup.example.com has a Preference of 20, so sending mail servers would try to connect to mail.example.com first, and backup.example.com second. You can have as many MX records as you want, and define the order of importance using their Preference values. If you have only one MX record, the Preference value does not matter.
Creating MX records in Dyn Standard DNS
For more information on creating MX records in Dyn Standard DNS, please see our article on receiving email with Dyn Standard DNS here.Creating MX records in Dynamic DNS
Dynamic DNS hosts allow you to set mail delivery options under the Mail Routing section. By default, Dynamic DNS hosts have no MX records. If you select Yes, let me configure Email routing, you will be given the following options:- MX Hostname: This is the host record of the destination mail server. Remember, you cannot use CNAMEs or IP addresses in this field.
- Primary: Yes, use it as my primary mail relay: A single MX record will be created for your Dynamic DNS host, assigned to the MX Hostname.
- Primary: No, use it as backup MX record: A primary MX record will be created for your Dynamic DNS host, assigned to the Dynamic DNS host itself, and a secondary MX record will be created and assigned to your MX Hostname.
myhost.dyndns.org 60 MX 10 mx.mailserver.comIf you choose No, use it as backup MX record, the MX records would be:
myhost.dyndns.org 60 MX 5 myhost.dyndns.org myhost.dyndns.org 60 MX 10 mx.mailserver.comThe TTL value of these MX records is identical to the TTL of the Dynamic DNS host itself.
Common Mistakes
There are a few common mistakes that you should be aware of.Backwards MX Records
When creating an MX record for a second-level domain, such as 'example.com', make sure that you leave the Host field blank. If you want email for @example.com addresses to be delivered to mail.example.com, the following MX records would be:Correct:
example.com 43200 MX 10 mail.example.comIncorrect:
mail.example.com 43200 MX 10 mail.example.comIncorrect:
mail.example.com 43200 MX 10 example.com
Caching Errors
By default, MX records created for Dyn Standard DNS hosts have a Time To Live (TTL) value of 12 hours. If you change the MX records for your domain, sending mail servers may continue to try to deliver email using the old information for up to 12 hours, until the records clear and the new information is retrieved. If you have just changed your MX records and you are receiving bounced messages or other errors, you may need to wait for the changes to propagate completely before mail is delivered correctly."The MX entered ("_") did not resolve or resolved to a CNAME."
If you are entering MX records provided by your mailhosting provider and you receive the above error, your mailhosting provider likely gave you CNAME records instead of host (A) records. MX records should only ever use host records for destination mail servers, and not CNAME records or IP addresses directly. (This rule is discussed in RFC 1035.)CNAME records are aliases for host records. To fix the problem, simply enter the host record itself rather than its CNAME.
Enter the destination mail server record into the Domain Name field and click Perform Query. The first item under the ";;ANSWER SECTION" will show you the actual host record. For example, smtp.secureserver.net is an alias for the smtp.where.secureserver.net record, which the tool shows as:
;; ANSWER SECTION: smtp.secureserver.net. 300 CNAME smtp.where.secureserver.net.
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