Provider error when sending email with large attachments for some Microsoft accounts

We've confirmed with Microsoft that this disruption stems from an issue on their end – specifically, an authentication misconfiguration impacting the data attachment service. Microsoft estimates around 50% of users leveraging this specific functionality might be impacted. Microsoft is implementing a solution, with a target resolution timeframe of Tuesday, April 22nd, 2025. We understand this may disrupt your workflow and are monitoring the situation closely. Further updates will be posted here.