Many companies use Microsoft 365 / Exchange Online, but use other email solutions such as CRM systems, security solutions or encryption gateways in parallel. Our product SecuMail Encryption, which is based on SeppMail , can also be easily integrated with Microsoft 365.

Until now, emails from Microsoft 365 were provided with a customer-specific identifier in the email header, the X-MS-Exchange-CrossTenant-id header. This allowed us to create customer-specific configurations and ensure that client separation is guaranteed even across system boundaries.

A few days ago, Microsoft started to stop providing this information to some of its customers, which led to the following error on the part of our S/MIME gateway:

Could not find a 'X-MS-Exchange-CrossTenant-id' header, mail will be rejected

There is a workaround, and at the same time SeppMail is working on a permanent solution. If your Microsoft 365 environment is affected by this (i.e. mails via the S/MIME gateway do not reach the recipient), please contact support immediately (support@secumail.de)