Exchange Online Outage, NDR Errors, & Delays in Mar ’25

March has been a shaky month for Microsoft as throughout the last week, many organizations and users have been experiencing an Exchange Online outage. The surprising part is that there were not one but two separate but related incidents tagged under the codes EX1027675 and EX1030895 that prevented users from sending emails.

The main problem that the majority of the affected people complained about was seeing an NDR alert (554 5.6.0) whenever they sent out a mail.

So to help you figure out what going on we have put together the latest updates on the outage(s), their symptoms, and what you can do at both personal and organizational levels. Let us first go over the timeline and current status of the issues.

When Did the Two MS Exchange Online Outages Start and What’s their Current State?

As mentioned before Microsoft’s cloud email system Exchange Online experienced two separate incidents that degraded the service capacity. Readers need to figure out which issue is ongoing and which one has been fixed.

When admins visit the service health message center in their M365 admin account they can see the following.

EX1027675 is Mostly Resolved:

This was the culprit responsible for the week-long MS Exchange Online service outage that began on March 7, 2025, around 12:30 PM UTC.

Ordinary users faced delays in sending their emails and sometimes got Non-Delivery Reports (NDRs) indicating that their message was not sent.

Microsoft took a while to respond but deployed a fix on March 14. That undos the code issue which was introduced in a recent update to message transport services. However, this was not the end of problems as another issue crept in.

The EX1030895 error is still Ongoing as of March 17, 2025:

This incident began on March 9, 2025, at 12:07 PM the main reason why it was overlooked was that it produced nearly identical symptoms of the other issue. Which is users receiving the NDRs with the “554 5.6.0 Corrupt message content” error one difference was that some attachments like calendar invites appear as plain text with winmail.dat attachments instead of their regular format. This specific Microsoft 365 Exchange Online outage only affects a smaller subset of messages. The good news is Microsoft is actively working on a targeted fix and performing restarts of affected servers.

If you are still experiencing issues or want to report something diffrent you can fill a Microsoft support ticket from your admin account.

Despite there being two different issues there is a significant overlap in the disruption of service let see what they are in more detail.

List of Common Problems During the Exchange Online Outages?

Most reported Exchange Online problems on public forums include:

• Email delays and failures
• Multiple Non-Delivery reports

This happened irrespective of the file type, large images, PDFs, or spreadsheets the moment they were attached to a mail they would not exit your mailbox. Even no text emails with just a send address and attachment fail to deliver. However it was found that if somehow users were able to reduce the size of attachments either by zipping or by splitting the mail delivery was possible.

Apart from regular attachments calendar invites also resulted in NDR. Sometimes the only thing the recipient got was an empty unusable winmail.dat file. To bypass this calendar details were being sent in text-only format.

Both external and internal emails were facing disruption during the Exchange Email outage. The same was the case for forwarded mail.

It was also seen if you had too many recipients in your to/cc/bcc fields then there was a high chance of failure. Distribution lists helped but were not the proper solution.

One interesting point was that newer users might have been hit harder. However, there was not much evidence to point to this. Maybe because of a lack of experience with Outlook/Exchange Online, they were not able to use the alternative mechanisms.

Workarounds and Solutions to the Current Problem

Here is a list of solutions we found to help people still having trouble with Exchange Online email communication.

Resend Emails: It is possible that your email may not have gone through because of another mistake like the wrong receiver address. So check all the details again and hit send.

Compress Attachments: If attachments are critical to the topic you are communicating then one option that is found to be working is zipping the file. All computers have the option to zip files/folders use them attach the compressed data to your email and hit send. Some large email sizes may still fail so we suggest that you split it into multiple small parts and send them one by one.

Microsoft has a strict service update schedule, especially in times like outages so keep an eye on the Service Health status.

Although it is mainly a sender-side issue ask your senders to switch off the Rich Text formatting. Use HTML/Plain text instead.

If problems persist, or you see some other symptoms unique to your case it would be better to open a Microsoft support ticket.

This Exchange Online Outage is Not the First (And May Not Even be the Last)

We say so because the service disruption that users were put through between (10 to 14) was seen as a continuation of the global Outlook outage that happened earlier around March 1st.

The error with the tag MO1020913 was a result of a “problematic code change,”. It not only disrupted Outlook but also took down many sister services like Teams, Microsoft 365, and even Azure.

Microsoft has said that the current issue is due to a separate reason. Nevertheless, for the end user, it hardly makes a difference. Last time they were unable to access the service this time they are unable to use it. These recurring self-induced outages too within such a short timeframe raise concerns about the stability of Microsoft’s services. So users began searching for alternatives like migrating from Office 365 to Google Workspace.

What Should Admins Do Before Exchange Online Down?

There are a few well-regarded industry best practices that can give organizations some respite during these kinds of scenarios. Among them, one particular procedure stands out. That is to construct a backup of organizational data.

Admins can save time and effort during backup formation by using the SysTools Office 365 Backup software. This solution has a long list of features

You can backup emails, contacts, calendars, and even OneDrive documents. Data kept offline is available in perpetuity whether there is an outage or not.

Moreover, the data restoration feature allows admins to deposit back the data into the same account. This is particularly useful if cloud-based data becomes corrupt.

Although the tool can’t prevent the outage from happening it makes it so that you face minimum impact. Even if the service ever goes down in the future without warning.

Conclusion

Here we say the steps users can perform to combat the Exchange Online outage. From their end like zipping up attachments or adding them in the form of a OneDrive shared link. Moreover, this once again clarifies why Microsoft or any cloud service provider for matter does not guarantee 100 % uptime. So that is why organizations should maintain a separate on-premise backup scenario like the one we introduced in this post. So safeguard your organizational data against such unpredictable downtime.