How to create a rule to know send a mail if a file is modified

Hey Christophe

Thanks For connecting Microsoft 
You can follow below step 

1. Go to Your SharePoint Document Library
   • Open the SharePoint site and navigate to the document library containing your file(s).
2. Select the File or Library
   • For a single file: Click the checkbox next to the file.
   • For all files: Do not select any specific file.
3. Click on “...”, then “Alert Me”
   • On the top menu, click the three dots (...), or in the menu bar, look for Alert Me.
4. Set Alert Settings
   • Choose Alert Me When Items Change.
   • Enter your email address.
   • Configure alert settings (change type, frequency, etc.).
   • Click OK.

You’ll now get an email when the file (or files in the library) are edited.

NOTE :- Starting July 2026, SharePoint Alerts will be fully retired, and Alerts will stop working.
            https://aka.ms/retirement/alerts/support

Also there is 2 Method

1. Go to https://flow.microsoft.com/
2. Create a New Flow
   • Select Create > Automated Flow.
   • Name your flow, e.g., “SharePoint File Edit Alert”.
   • Choose trigger: When a file is created or modified (properties only).
3. Configure the Trigger
   • Site Address: Your SharePoint site.
   • Library Name: Your document library.
4. Add an Action
   • Action: Send an email (V2).
   • Enter your mailbox address and customize the message.
   • You can include dynamic content (file name, editor, etc.).
5. Save the Flow

You’ll now get an email every time any file is edited in the library!