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How Nylas Sends Emails

Nylas does not send emails from our servers. Instead, we hand off the message to your outbound SMTP email server for delivery. Handing off the message ensures all email authentication records like SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mails), and DMARC (Domain-based Message Authentication, Reporting and Conformance) are still aligned to you for maximum email deliverability.

Usually, if you were using a new email sender, you would need to update your DNS records and other mail settings to authenticate the new server. Then you would have to go through the process of warming up your server. Since Nylas uses the existing SMTP server, we can leverage your existing reputation and authentication.

When you use the Nylas API to send an email, we will attempt to POST that email to the SMTP server. If there is an error response from that server, we will return the response error code in the API response. If the SMTP server accepts the email, we return a 200 (success) response. A successful response doesn't mean the email was delivered successfully; it means that your SMTP server accepted the email for delivery.

If the SMTP server is under a heavy load, the response time can be delayed. We recommend having a large timeout for /send calls.