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How Salesforce Uses MX Records for Email Delivery

Publiceringsdatum: May 29, 2026
Beskrivning

What Are MX Records and How Does Salesforce Use Them?

When Salesforce sends an email, it uses DNS (Domain Name System) to look up the MX (Mail Exchange) records for the recipient's email domain. MX records specify which mail servers accept incoming email for that domain.
For example, when sending to test@salesforce.com, the Salesforce MTA (Mail Transfer Agent) performs a DNS lookup for the salesforce.com domain, finds its MX records, and attempts an SMTP (Simple Mail Transfer Protocol) connection to the mail server with the lowest MX priority number.

Checking MX Records

You can check MX records from most machines using a command-line DNS lookup. However, command-line results reflect the DNS view from your local network, which may differ from what is visible to users on the public internet.
To validate a global view of MX records, use an external tool such as MXtoolbox (see Additional Resources).
This information applies to both Lightning Experience and Salesforce Classic.

Lösning

How MTAs Use MX Record Priority

MTAs (Mail Transfer Agents) always attempt delivery to the MX record with the lowest preference number first. If delivery to that MX record fails, the MTA tries the next record in the list with the next highest preference number.

Retry Behavior When Delivery Fails

When an MTA cannot deliver to any legitimate MX record for the domain, it retries delivery at increasing intervals. Retry periods typically range from approximately 4 hours to 72 hours, depending on how the sending MTA is configured. Salesforce MTAs retry delivery for up to approximately 24 hours.

Email Relay and MX Records in Salesforce

If your organization uses email relaying in Salesforce, Salesforce MTAs do not use standard MX record lookups for delivery. Instead, they send email only to the MX record, hostname, or IP address specified in the Email Relay settings in Salesforce.
Best practice: Use an MX record (not an IP address) in the Salesforce Email Relay settings. An MX record provides redundancy by pointing to multiple mail servers, whereas a hostname represents only one specific MTA with no failover.

Knowledge-artikelnummer

000386476

 
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Salesforce Help | Article