Resolved: Microsoft Outlook Blocking All Email from Domain as Spam.

Update: Emails from no longer go to Spam in Outlook.

2023-12-06 / First published: 2023-12-05
Microsoft is filtering the entire email domain as spam.
It's amazing how quickly Microsoft can fix things if issues are made public: Yesterday we've reached out to Microsoft Germany along with the press release asking them - again - to fix the issue of emails going to Spam in Outlook. The issue was then fixed within one day (after we had been in direct contact for three weeks without any success)!

What Happened?

Our users were reporting that their emails sent to Outlook are marked as Spam since mid of November until beginning of December. While at first we thought this to be an isolated issue, we soon realized that this issue affected all emails sent from any email address. The issue was still not resolved three weeks later, so we made it public with the following post.

To us this process is just another proof that Big Tech is able to solve such issues, but unwilling to do so for just 'any company'. I'm sure there are many more, smaller companies that face similar issues and that are not able to reach out to the press or have other means of making such issues public.

That's why Big Tech as gatekeepers need to be checked more thoroughly. Even if the cause if a technical issue, Big Tech must be held accountable and must fix such issues in a reasonable amount of time - when asked, not when the press starts talking about it!

Original Post

Since mid November, our users are reporting that their emails sent to Outlook are being flagged as Spam. This affects all emails sent from any email address. Our team reached out to Microsoft’s support team as well as to our direct contact, a board member of Microsoft Germany. However, the issue has yet to be resolved.

“We repeatedly tried to solve the issue with Microsoft, but unfortunately the Microsoft support team has only replied with standard emails. The issue has not been solved to date so we contacted a board member of Microsoft Germany on 27 November, but have not heard back to date”, says Matthias Pfau, co-founder and CEO of Tuta.

Last year we experienced a similar situation related to Tutanota accounts being unable to sign up for Microsoft Teams and the issue was only resolved after making it public.

Microsoft Outlook Blocks All Email from Domain as Spam.

In mid November 2023 the technical support team at Tuta began receiving emails from customers reporting that they were encountering falsely applied spam filters when trying to send emails to Outlook users from addresses.

Other Tutanota email domains such as,,, and are not affected, yet, the issue is still not resolved. By now it has become apparent to us that Microsoft is blacklisting the entire domain as spam.

Our technical support team first reached out to Microsoft on November 16th, 2023, and received the following response:

Initial Outlook Support Email

After informing Microsoft of these email delivery errors and the incorrect marking of emails as spam, Microsoft Support responded with the unrelated reply that there are no problems with our IP addresses. At this point we requested that this case be escalated.

On November 20th, 2023 we received another boiler plate response from the Microsoft support team informing us that there are no active blocks of our server IP addresses, but there were some emails which were being filtered on their end which had been flagged as spam. They also informed us that we are eligible for a "temporary mitigation" and that this process can take 24-48 hours.

We expected that this fixed the issue - but it didn't.

Followup Outlook Support Email

Following this email, we contacted Microsoft again on November 24th as this incorrect spam filter is still being applied to email addresses. They replied on the same day, again asserting the claim that our IP addresses are not being blocked.

I myself reached out to a board member of Microsoft Germany requesting further assistance in resolving this error, but to date have received no further response.

At the time of writing, December 5th 2023, this issue continues to persist. After having tried to resolve this technical error through the standard designated support process to no avail, we are making this issue publicly known.

Big Tech Needs to Take on Responsibility

It cannot be that Big Tech can make such mistakes and fail to address them. These errors are causing problems not only for Tuta and our reputation, but also for our customers.

Businesses using Tuta will regularly be in contact with people and businesses using Outlook, and if their emails are being incorrectly flagged as junk mail this will hurt them. Big Tech needs to be held accountable for the consequences of such errors.

These kinds of practices violate the spirit of the EU's Digital Markets Act (DMA) which already names Microsoft, among other tech giants, as playing the role of "gatekeepers". Tuta currently has over 10 million users worldwide and Microsoft's incorrect labeling of our domain as spam impacts any of them who might be trying to contact someone with an Outlook account. Big Tech needs to play fair and keep internet traffic neutral and open - also the email traffic.

Current Status

Currently, emails sent from a Tuta account using the email domain are being incorrectly sorted into the junk mail folder when they arrive in the mailbox of an Outlook user.

What Tuta Users Can Do Now

We are working hard to get this issue resolved as quickly as possible. We are certain that Microsoft will solve this issue rather quickly once it reaches a critical mass of publicity (as they have done in the past).

If your emails from are affected by this issue, please contact your friends and colleagues on Outlook to whitelist your emails. This way you will help the Outlook spam filter to learn that emails from addresses are not spam. We at Tuta keep spammers out of our system and block suspicious accounts immediately. Thus, we have a very good sender score. Emails from are not going to spam on Gmail, Yahoo Mail or any other major email services.

If you are paying user of Tuta and this issue is impacting you or your business, we recommend that you create an email alias using another domain. We highly recommend choosing because it is only available to paying customers and is therefore less likely to be affected by spam blocks.

We urge the team at Microsoft to get this resolved!