Extended notification - Email content truncated outside of SAP

Hello SAP community,

We would like to use extended notification to validate WF items.

Program SWN_SELSEN is generating email notification with approval/refusal link (validation in BSP page).

In SOST, email format is good, links are working properly -> everything is fine.

Outside of SAP in Outlook, email is truncated and we only have few details.

Any ideas of what could cause this issue?