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550. 5.7.1 Unconfigured Sending Domain

Last updated February 2020

A sending domain is a domain that is used to indicate who an email is from via the From: header. Using a custom sending domain enables you to control what recipients see as the From: value in their email clients. DNS records can be configured for a sending domain, which allows recipient mail servers to authenticate your messages. The Sending Domains API provides the means to create, list, retrieve, update, and verify a custom sending domain.

Improperly Configured Sending Domain

If you receive the following error message 550 5.7.1 Unconfigured Sending Domain as a response when sending a transmission, it is because you used a from address whose domain is not one of the sending domains that you created in your account.


If I use as my message's from address, but the only sending domain in my account is, I will receive a 550 5.7.1 error message when I make a transmission with the REST API or SMTP relay.


Changing the from address to will correct the error, because is a configured sending domain.

Additional Information

Refer to this Knowledge Base Article to learn more about how to configure Sending Domains.

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