关于能否通过Outlook REST API更新他人邮箱签名的技术问询

Great question—let me break this down clearly since the old docs and outdated resources can be confusing:

First, a critical note: the Outlook REST API has been officially deprecated and replaced by Microsoft Graph API—this is exactly why you’re not finding up-to-date info in official docs anymore. Microsoft no longer maintains or updates the Outlook REST API, so those 2-3 year old resources you found are referencing a legacy system that’s now phased out.

To answer your core question: Yes, you can update another user’s email signature, but you’ll need to use Microsoft Graph API instead of the old Outlook REST endpoint, and you’ll need the right permissions in place:

• If you’re building an application that acts independently (not on behalf of a specific user), you’ll need the MailboxSettings.ReadWrite.All application permission. This requires admin consent in your Azure AD tenant.
• If you’re acting on behalf of a user (delegated permission), you’ll need MailboxSettings.ReadWrite—but the delegated user must have appropriate admin privileges (like Exchange Online Administrator or Global Administrator) to modify other users’ mailbox settings.

The specific Graph API endpoint to use is a PATCH request:

PATCH /users/{user-id}/mailboxSettings/signature
Content-Type: application/json

{
  "signature": "<div>Your updated HTML-formatted signature here</div>"
}

Just to recap: Ditch the old Outlook REST API—Microsoft Graph is the supported, up-to-date way to handle this scenario now. Make sure you’ve set up the correct permissions and are targeting the Graph endpoint (not legacy Outlook REST URLs) to get this working reliably.

内容的提问来源于stack exchange，提问作者Adam McGurk