I'm running Lotus Notes Client v8.5.3 on Windows XP and Apple MAC 10.5.8
After a clean up and archive to remove 75% of my email notes to archive database I notice the mail file is still 180Mb in size.
On further investigation I see the local mail file copy is still using ODS 43.
Most technotes I find describe how to convert an NSF database to ODS 51 using Compact -c on the Domino Server. Problem with this is I don't have access to the Domino mail server.
A little hunting around and I find a really useful technote :
How to handle ODS database versions in mixed Notes environments.
To convert to ODS version 51 = Notes 8.5 database format using the Notes 85 Client you just need to create a new replica/database using the .N85 extension, rather than .NSF extension.
My resulting mail file shrunk from 180Mb down to 102Mb.
Its also worth pointing out that the ODS version do not replicate. So its possible to have multiple replicas of the mail file with different ODS versions.