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Email Signature Server - Unsupported Use Cases

There are some email use cases that are not supported with Email Signature Server due to Microsoft, other technical limitations, or they are unsupported by specific design decisions. Below are the tables listing these various use cases with some remarks on the nature of the limitation.

  Prerequisites

  • Templafy Email Signature Server.

  Note

Templafy Email Signature Server will not stamp email signatures in any of the cases below.

By Design

Case Remarks
Connector validation message Sender is O365ConnectorValidation
Message is Exchange calendar item Contains header "X-MS-Exchange-Calendar-Series-Instance-Id"
Message contains calendar item Signature placement here is undesired
Auto-generated message Contains header "auto-generated"
Auto-reply message Contains headers "x-autoreply", "x-autorespond", "auto-replied"
Read receipt messages "message/disposition-notification" message types
Microsoft Planner comments  Signature placement here is undesired
TNEF messages not marked as Email Message documents When using TNEF as communication format, the message parsed might have different types. We are only considering the signature attachment for Email Messages
Plain Text Already processed by Templafy Contains header "X-ProcessedByTemplafy"
RTF Already processed by Templafy Contains header "X-ProcessedByTemplafy"
HTML Converted from RTF Already processed by Templafy Contains header "X-ProcessedByTemplafy"

Due to Technical Limitations

Case Remarks
Encrypted message S/MIME and PGP/MIME protocols, no signature
End to end signed message S/MIME and PGP/MIME protocols, no signature
Microsoft Information Protection labeled and encrypted messages No signature, can use "msip_labels" mail flow rule
RTF messages that do not provide the HTML version For RTF, we request the HTML version using Graph API. In cases where this request fails, no signature can be added
Out of office / automatic forwarded emails with external forwarding feature enabled Messages are sent but broken with winmail.dat attachment
Out of office with external forwarding disabled Emails are being blocked
RTF reply to email Signature attached at the bottom
Recall emails functionality fails

Recall email function is itself implemented as an email. When these special Recall emails are forwarded to any Outbound Connector, the Recall functionality will fail. Can use mail flow rule bypass.

Additionally, any email forwarded to any Outbound Connector will not be able to be recalled later.

Active Security Feature

Case Remarks
Templafy secret key validation fails RelayDenied response
DKIM verification fails TransactionFailed response

  Note

When sending RTF emails with in-lined images, the image quality is lost and the HTML format is broken. This is not related to Email Signature Server as it can be reproduced in any Microsoft 365 environment.

ESS tech_role
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