The company I work for (25friday.com) has been hit with what seems to be a keyword blacklist on Microsoft 365 email.

In short, if we send out any email to clients using Microsoft 365 as their email provider containing the textual content "25friday.com" anywhere on the email subject, body or readable attachment (e.g. pdf) the emails fall on a "blackhole" and are neither bounced nor reaching the recipient (they are not in spam or quarantine either).

As you might imagine this is a huge problem for us as email is our primary means of communication with our clients and we need to be careful to never include any mention of our domain in any email we send to them.

For recipients using personal Outlook emails, the emails are received and sent to spam with a spam score of 9 (maximum score).

We've reached Microsoft support and they seem as clueless as we are. They have no idea why this is happening and they are unable to provide any information or progress on the ongoing issue. This has been going on for about a month now.

A few things we have tried:

- We have checked our SPF, DKIM, and DMARC records and they are all set up correctly and passing.

- We have checked our email sending reputation and it is good as far as we can tell.

- We have tried sending emails from different email addresses and domains, but the issue persists.

- We have setup our own Microsoft 365 account to be able to submit false-positive reports on the security portal, but the submissions disappear into the void and we never receive any feedback.

- We have tried some deliverability testing tools and they all report that our emails are being blocked by Microsoft 365, but not by any other email providers.

- We are not on any known/public blacklists

Note that we are using Google Workspaces, but that does not seem to be the issue. The domain itself has been live since 2018 (since the company was founded) and we have never had any issues with email deliverability before. We don't send spam or unsolicited emails. The closest I could think of is a mailing list we have with about 300 subscribers containing mostly client emails but also some emails of people we invite to our events. We send out an approximately monthly newsletter to this list, but we have never had any complaints or issues with it before (we're using Pipedrive for that).

Tangential but I believe that it might be related: if I set my website address as 25friday.com on my LinkedIn profile, the link gets overwritten to a LinkedIn error page. My guess is that since LinkedIn is owned by Microsoft, they are sharing the same blacklist.

Any tips would be greatly appreciated. We're really affected by this and without any recourse to escalate this issue.