[Bug]: "Failed to create share" when using email address for internal user + [Feature Request] Email notification for internal shares #65999

Bug description

When attempting to share a file or folder with an existing internal user by typing their registered email address, the sharing dialog's autocomplete successfully resolves and displays the correct internal user. However, upon confirming the share, the operation aborts with a generic "Failed to create share" error.

This is problematic because:
It completely blocks a valid internal share.

I hope when this will work the internal users should ideally receive email notifications for shares as it happens with external users.

Steps to reproduce

1. Log in to Nextcloud Hub 26 Summer (35.0.2).
2. Navigate to the Files app and select a file/folder to share.
3. Open the sharing sidebar and start typing the email address of an internal user (who already has an account on this instance).
4. Observe that the system's autocomplete successfully recognizes the email and displays the internal user in the dropdown list.
5. Select the user from the dropdown and confirm the share.

Expected behavior

Share should have success and send an email alert to the internal user

Nextcloud Server version

35

Operating system

Debian/Ubuntu

PHP engine version

PHP 8.5

Web server

Apache (supported)

Database engine version

MariaDB

Is this bug present after an update or on a fresh install?

None

Are you using the Nextcloud Server Encryption module?

Encryption is Enabled

What user-backends are you using?

• Default user-backend (database)
• LDAP/ Active Directory
• SSO - SAML
• Other

Configuration report

List of activated Apps

Nextcloud Signing status

Nextcloud Logs

Additional info

No response