Tienes activado el Shared Mail en el servidor?? Parece como si algun documento con anexos estuviera vinculado al Shared Mail y se hubiera perdido el link

revisa esta nota http://www.ibm.com/support/docview.wss?uid=swg21313756

Resolving the problem

This mail file was a shared mail file at one point but is no longer.  Perform the following commands ont eh server console:

1.  load object unlink mail\<database.nsf>  to unlink the database as a shared mail database.
2.  load object Collect mail\<database.nsf> to remove any documents that are linked to the shared mail database.
 

Saludos