How is DNS resolved for email addresses

domain-name-systememail

If I send an e-mail to gus@example.com, how does my e-mail client find out what IP address to send the e-mail to? I understand it would do a DNS lookup for example.com, but I want to know what records would be used exactly.

I can send e-mail successfully to one of my domains, gus@echochess.com, and there are no MX records. I am assuming it is using the A record here, but what if I wanted to have a different mail server handle emails, with a different IP?

Best Answer

The answer is in RFC 5321

The lookup first attempts to locate an MX record associated with the name. If a CNAME record is found, the resulting name is processed as if it were the initial name. If a non-existent domain error is returned, this situation MUST be reported as an error. If a temporary error is returned, the message MUST be queued and retried later (see Section 4.5.4.1). If an empty list of MXs is returned, the address is treated as if it was associated with an implicit MX RR, with a preference of 0, pointing to that host. If MX records are present, but none of them are usable, or the implicit MX is unusable, this situation MUST be reported as an error.

To make it a bit more human-readable, and assuming the domain example.com:

Mailserver asks for an MX-record for example.com
a. If there is one or more MX-records, choose the one with the lowest preference. Remember this for step 3.

b. If there isn't one, ddecide that example.com is acting MX record with lowest preference. Remember this for step 3.
Resolve the MX record to its matching A record and contact that host

So as long as you don't have a specific MX record, your A record will be used as an MX record. Once you do setup an MX record, that one will be used instead.

Related Solutions

email – How to Send Emails and Avoid Spam Classification

Be sure that your emails don’t look like typical spam emails: don’t insert only a large image; check that the character-set is set correctly; don’t insert “IP-address only” links. Write your communication as you would write a normal email. Make it really easy to unsubscribe or opt-out. Otherwise, your users will unsubscribe by pressing the “spam” button, and that will affect your reputation.

On the technical side: if you can choose your SMTP server, be sure it is a “clean” SMTP server. IP addresses of spamming SMTP servers are often blacklisted by other providers. If you don’t know your SMTP servers in advance, it’s a good practice to provide configuration options in your application for controlling batch sizes and delay between batches. Some mail servers don’t accept large sending batches or continuous activity.

Use email authentication methods, such as SPF, and DKIM to prove that your emails and your domain name belong together. The nice side-effect is you help in preventing that your email domain is spoofed. Also check your reverse DNS to make sure the IP address of your mail server points to the domain name that you use for sending mail.

Make sure that the reply-to address of your emails are a valid, existing addresses. Use the full, real name of the addressee in the To field, not just the email-address (e.g. "John Doe" <john.doe@example.com> ) and monitor your abuse accounts, such as abuse@example.com and postmaster@example.com.

Domain – How should I setup separate MX records for a subdomain

You should never point your MX to a IP address to be RFC compliant. Make an A record for the IP address instead and point the MX record to it.

Then the zone should look like this,

    @               IN      MX      1       ASPMX.L.GOOGLE.COM.
    @               IN      MX      5       ALT1.ASPMX.L.GOOGLE.COM.
    @               IN      MX      5       ALT2.ASPMX.L.GOOGLE.COM.
    @               IN      MX      10      ASPMX2.GOOGLEMAIL.COM.
    @               IN      MX      10      ASPMX3.GOOGLEMAIL.COM.
    @               IN      MX      10      ASPMX4.GOOGLEMAIL.COM.
    @               IN      MX      10      ASPMX5.GOOGLEMAIL.COM.
    @               IN      A       10.24.233.214
    mailer          IN      A       10.24.233.214
    mailer          IN      MX      10      mailer.cranketywidgets.com.

Best Answer

Related Solutions

email – How to Send Emails and Avoid Spam Classification

Domain – How should I setup separate MX records for a subdomain

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