I'd assume the archive is copying the doc. That creates a new ID for the document.

Hello Mike,

Thank you for your reply.

So I presume the links have to be mapped again manually.

It'd depend on how the email was archived & how OneNote represents the link.

For simple doc copies, the first archival copies of a document still have the same lower 16 hex digits, but the upper ID has often been changed (normally to the DBID of the archive DB). This gets rebuilt entirely though if the document is copied a second time, even if the first is deleted: in that case the document gets a new UNID.

If the backup server is making a replica, the database and the doc IDs would remain the same, but the server would change.

I assume the link is already a URL "or something", in which case it would need to be modified to change the database or the server anyway.

I couldn't tell you more without knowing more about the OneNote link & whether it stores the server name, the DB name, or the UNID