A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
Hi @ZTS
The Optional Message field in the SharePoint Online/OneDrive sharing dialog is limited to 500 characters. This is a service limitation and cannot currently be increased. As a workaround, you can share the file first and then send a separate email or Teams message containing the full details and the sharing link.
I have not been able to locate an official Microsoft documentation page that explicitly states the 500-character limit for the Optional Message field when sharing files in SharePoint Online or OneDrive.
However, the limitation is visible directly in the sharing dialog. In the screenshot provided, the message field displays a counter of 490/500, indicating that the maximum supported length is 500 characters.
I also found an existing Feedback Portal suggestion requesting an increase to the sharing invitation message character limit: Increasing Message Character Limit
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