Update - Update from Microsoft:

The cause of the issue has been identified, and a fix has been rolled out. It is expected to be fully deployed by early next week. We apologize for the disruption this has caused.

We will continue to monitor the situation and provide further updates as needed. Thank you for your patience.

Apr 18, 2025 - 12:11 PDT
Update - To mitigate Microsoft's bug that only impacts attachments sent using multipart/form-data, we recommend using application/json instead for attachments under 3MB. This workaround will continue to work effectively even after Microsoft resolves their bug.

For more details, please refer to Nylas’ official guide:
Sending attachments < 3MB via JSON (Nylas API v3)

Apr 18, 2025 - 10:34 PDT
Update - We have escalated the bug ticket to the highest priority with Microsoft Office 365. However, at the time of this update, they have only acknowledged receipt of the issue. We are actively working to get a response and status update from Microsoft, but they have yet to make a public acknowledgment.

The number of users and organizations reporting these errors—particularly when sending larger attachments via the Graph API—on public Microsoft forums continues to rise. For reference, here is one of the public threads:

https://learn.microsoft.com/en-us/answers/questions/2258885/graph-api-createuploadsession-returns-401-on-uploa

At Nylas, we are exploring potential solutions to help mitigate these errors for our customers while Microsoft works on a fix. We will update this page as soon as we have progress to share.

Apr 18, 2025 - 09:06 PDT
Update - We are still waiting on a response from Microsoft to our support ticket, but continue to find other MS Graph users facing the same errors from MS starting today:

https://learn.microsoft.com/en-us/answers/questions/2258994/issue-with-sending-emails-with-large-attachments-v

Apr 17, 2025 - 12:25 PDT
Identified - We continue to investigate the root cause, however we are starting to see reports around the Internet of other Microsoft Graph users experiencing this net-new behavior and errors from MS. Below is one example:

https://learn.microsoft.com/en-us/answers/questions/2258885/graph-api-createuploadsession-returns-401-on-uploa

We are also opening a Bug Ticket with Microsoft.

Apr 17, 2025 - 09:46 PDT
Update - We have narrowed the impact of this incident to include only calls to Send for Microsoft Graph for emails with large attachments. We are continuing to investigate why Microsoft started returning these provider errors at approximately 1:00 AM today.
Apr 17, 2025 - 05:37 PDT
Update - We are still investigating the cause of this incident.
Apr 17, 2025 - 04:15 PDT
Investigating - We are investigating higher levels of 401 errors for email sending. This appears to be limited to Microsoft grants sending emails with attachments.
Apr 17, 2025 - 03:55 PDT

About This Site

Seeing issues that aren't reflected on this page? Contact us at support@nylas.com

Nylas Application Services Degraded Performance
API v3 ? Degraded Performance
Authentication v3 ? Operational
Dashboard v3 ? Operational
Scheduler v3 ? Operational
Webhooks v3 ? Operational
IMAP v3 ? Operational
Data Connectors v3 Operational
3rd Party Providers Operational
Microsoft 365 ? Operational
Outlook.com ? Operational
Yahoo! ? Operational
iCloud ? Operational
Cloudflare ? Operational
Google ? Operational
Mailgun ? Operational
Subprocessors Operational
* Subprocessor Change Notification ? Operational
AWS ? Operational
GCP ? Operational
&Open ? Operational
Atlassian Pty Ltd ? Operational
Apollo ? Operational
Coralogix ? Operational
Datasiv ? Operational
Docusign ? Operational
Drata ? Operational
Gong.io ? Operational
Google ? Operational
Google ? Operational
Honeycomb.io ? Operational
Hubspot ? Operational
Ketch ? Operational
Kong Inc. ? Operational
Looker ? Operational
Marketo ? Operational
Microsoft ? Operational
New Relic ? Operational
Recurly Inc. ? Operational
Retool Inc. ? Operational
Rootly, Inc. ? Operational
Salesforce ? Operational
SalesHood ? Operational
Salesloft ? Operational
Slack ? Operational
Stripe ? Operational
Tropic ? Operational
Twilio Segment ? Operational
Vercel ? Operational
Woopra ? Operational
Zendesk ? Operational
ZoomInfo ? Operational
Fastly ? Operational
Operational
Degraded Performance
Partial Outage
Major Outage
Maintenance
Apr 20, 2025

No incidents reported today.

Apr 19, 2025

No incidents reported.

Apr 18, 2025

Unresolved incident: Microsoft Graph Returning Intermittent 401 Errors for Sending Emails with Large Attachments.

Apr 17, 2025
Resolved - The incident affecting API v3 latencies for provider calls and webhooks has been resolved. All mitigations have been successfully implemented, and latencies have returned to normal levels. The backlog of pending webhooks has been cleared, and all systems are functioning as expected.

We will continue to monitor performance to ensure stability. Thank you for your patience and understanding.

Apr 17, 14:33 PDT
Monitoring - All mitigations have been implemented, and latencies continue to improve. Our systems are working through the backlog of pending webhooks. We will continue to monitor the situation closely and consider the incident resolved once all outstanding webhooks have been sent.
Apr 17, 13:43 PDT
Update - Latencies are beginning to improve as we continue deploying the mitigations. We will keep monitoring the situation and provide further updates as necessary.
Apr 17, 13:08 PDT
Identified - We have identified a potential root cause and are actively implementing mitigations to address the issue. We will continue to monitor the situation closely and provide updates as needed.
Apr 17, 12:35 PDT
Update - Our team is actively working on identifying the root cause and implementing mitigations. We will provide further updates as soon as we have more information. Thank you for your patience.
Apr 17, 12:10 PDT
Investigating - Starting at approximately 8:45 AM PT, we started to see increasing latencies for both Provider API calls and webhooks. We are investigating the root cause and working on mitigations and will post updates to this page.
Apr 17, 10:59 PDT
Apr 16, 2025

No incidents reported.

Apr 15, 2025

No incidents reported.

Apr 14, 2025

No incidents reported.

Apr 13, 2025

No incidents reported.

Apr 12, 2025

No incidents reported.

Apr 11, 2025

No incidents reported.

Apr 10, 2025

No incidents reported.

Apr 9, 2025

No incidents reported.

Apr 8, 2025
Resolved - Between 2025-04-08 14:00 PDT and 2025-04-08 18:04 PDT, customers may have experienced intermittent 503 errors across our services. This was due to an upstream incident affecting our subprocessor, Fastly.

To mitigate the issue and restore stability, we’ve rerouted impacted traffic from Fastly to Cloudflare. This change has fully resolved the incident.

We’re continuing to monitor closely and will conduct a full postmortem to ensure long-term resilience.
Thank you for your patience

Apr 8, 18:40 PDT
Monitoring - We incorrectly marked the earlier incident as resolved. The issue is still ongoing due to a third-party provider, Fastly. We are actively monitoring the situation and assessing any ongoing impact.

We sincerely apologize for the confusion and will post regular updates here as we receive more information

Apr 8, 17:00 PDT
Resolved - Fastly has posted the following update on their Status Page (https://www.fastlystatus.com/incident/377443):

"A correction has been deployed to the NGWAF platform by Engineering, resulting in a phased recovery for affected customers. Deployment monitoring will persist until full service restoration is observed for all impacted services.

This incident caused disruption to customers utilizing NGWAF services; all other products and services remained operational.

Customers experiencing ongoing issues are encouraged to contact their assigned account teams or the support team through dedicated support chat or email at support@fastly.com if a case is not already in progress."

Apr 8, 16:41 PDT
Update - Fastly has posted the following update on their Status Page (https://www.fastlystatus.com/incident/377443):

"Our engineers have identified the contributing factor and are applying a fix to our Next-Gen WAF (NGWAF) services."

Apr 8, 15:20 PDT
Monitoring - Some customers may be experiencing elevated 503 errors when accessing our services on API v3. This is related to an active incident at our CDN provider, Fastly. Our team is closely monitoring the situation and working to mitigate impact where possible.

You can track Fastly's progress on their Status Page here: https://www.fastlystatus.com/incident/377443

Apr 8, 13:48 PDT
Apr 7, 2025

No incidents reported.

Apr 6, 2025

No incidents reported.