Why do I get a lot of 'Updated' documents when I replicate

We have a number of users who replicate their mail daily and some of them are seeing extended replication times. When I check the local log.nsf on the client machine, I can see a high number (in some cases >3000) of updated documents that were initiated by the local mail file back to the server. None of these users generate this much activity.

As a bit of a newcomer to Notes, I am confused as to why I should be seeing so many updates - any help and advice appreciated.

TIA

Mark