When using server-side signatures, administrators may notice that signatures are not applied to certain internal emails. This typically occurs because of how Exchange Online formats messages sent within the same tenant.
Why signatures may not be applied
In some scenarios, Exchange Online sends internal emails using TNEF (Transport Neutral Encapsulation Format).
This usually happens when Exchange assumes that the message will be processed by another Exchange environment, such as when messages are sent internally within the same Microsoft 365 tenant.
Because TNEF is a proprietary Microsoft format, the Xink ReRouter ignores these messages by default. As a result, signatures are not added unless the message is converted to a standard email format.
How the Xink TNEF message handler works
To ensure signatures can still be applied, Xink includes a TNEF message handler that converts these messages before they are processed.
The handler performs the following steps:
- Unpacks the TNEF-encoded message.
- Converts the message into the standard MIME format.
- Processes the message through the normal signature injection workflow.
- Returns the processed message to Microsoft 365 in MIME format.
This conversion happens automatically and is not visible to end users. Emails will appear the same as usual, but signatures can now be applied correctly.
Important information
Server-side settings are cached within the email processing farm.
If you change configuration settings, it may take some time for the changes to be fully applied across the system.
