If the restrictions on message size are not properly set it is possible to flood a domino server with such large attachments it can start to eat up all server resources and impar domino's functionality.
Resolving the problem
Since the Daos process is event driven stopping the event in process will be sufficent, it will not attempt to daosify the attachment again. However there is no task that can be brought down to stop DAOS, the server must be brought down. If the server is clustered this can be done one cluster mate at a time while user's fail over. While the server is down look in the DAOS directory for large attachments created at the time the issue began. These can be removed.
Users who have the attachment and attempt to open it will produce messages on the console
The database Path\name.nsf attempted to access a missing file: Path\name.nlo: File does not exist
After the attachment has been removed from all servers the link can be removed from the mailfiles with the command fixup Path/name.nsf -J -D can remove the now bad links.
The DAOS catalog will need to be resynchronized after this, it is best to do so when the server is less busy/