Règle de signature de mail

Hi OlivierT185,

if I translated your question right, you can attempt the following steps to establish an organization-wide email signature in Microsoft 365:

1. Access the Microsoft 365 admin center and choose Exchange.
2. Navigate to Mail flow.
3. Select Rules.
4. Click on Add a rule and choose Apply disclaimers.

Implementing these steps will apply the signature to all messages. 

Create organization-wide signatures and disclaimers - Microsoft 365 admin | Microsoft Learn