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Developer Guide

Sending Failures

Message Delivery Submission Failed

  • Message delivery submission failed 120 - Microsoft
  • API Error 429 - Nylas

When attempting to send an email Nylas will sometimes receive a 120 error code from the Microsoft mail servers.

120 MailSubmissionFailed The server failed to submit the message for delivery.

When we receive this error from the mail provider, Nylas will return an HTTP 422 error code with the following message:

Message delivery submission failed

The Exchange logs might show:
MapiExceptionSendAsDenied: Unable to submit message.


Solution Delivery Submission Failed

  • Check the sending name. Make sure the sending email is the same as the synced account.
  • Retry the send with exponential backoff.
  • Confirm that the Exchange server has not quarantined the syncing devices we use to sync.
  • Settings should match our Suggested Office 365 Settings.
  • Reach out to the mail provider to get more information about the issue.

The issue is that occurs on a small number of hosted Exchange and Office 365 servers. Unfortunately, since it is on a server outside of our control, we aren't able to diagnose the issues

Related Guides

Other errors related to sending failures:

Updated 9 days ago

Sending Failures

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