Passwordless Email Code Delays and Missing Emails via Custom Provider (SendGrid)

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Hi Auth0 Community,

We’re encountering issues with passwordless login (code-based) using a custom email provider (SendGrid via API) in our EU tenant.ifying_glass_tilted_right: First try searching for your answer.

:warning: Issue 1: Email Code Delivery Delays Leading to Expired Logins

  • Auth0 logs show the email code was “sent” (type: cls) at T₀.
  • SendGrid logs show the same message was processed ~2.5 minutes after T₀.
  • Emails arrive promptly after SendGrid processes them, but by that time, the one-time login code is already expired.
  • This delay happens even under low system load.
  • We’ve updated the passwordless code expiration time to mitigate the issue, but this seems like a workaround rather than a fix.

We suspect there may be queuing or throttling within Auth0 before the message is handed off to SendGrid.

:warning: Issue 2: Emails Marked as Sent by Auth0 but Missing in SendGrid

In a few instances:

  • Auth0 logs (type: cls) indicate that the code email was sent.
  • However, the corresponding email does not appear in SendGrid analytics (no processed, delivered, or bounced events).
  • The affected addresses are not suppressed, bounced, or invalid in SendGrid.
  • No email_sending_failed or fapi logs were present in Auth0 for those cases.

This suggests a possible silent failure or drop between Auth0 and SendGrid, despite the successful cls log entry.

:magnifying_glass_tilted_left: Summary of Actions Taken

  • Confirmed SendGrid API integration is active and responsive.
  • Checked for suppression/bounce issues — none found for affected recipients.
  • Verified that email_sending_failed logs are absent in these cases.
  • Increased the passwordless code TTL, which reduces the impact of delay but does not address root cause.

:person_raising_hand: Questions

  1. Could Auth0 be internally delaying or queuing emails before sending to SendGrid?
  2. Are there cases where an email could be marked as sent (cls) but never reach the email provider?
  3. Are there known issues or limitations when using SendGrid via API for passwordless code flows?
  4. Is there a way to enable more visibility into the email sending process (e.g., pre-send logs, retries, failures)?

I’d appreciate any insights or guidance to help me resolve this or improve reliability and observability of my passwordless login emails.

Thanks in advance!

—
Ilya