Interesting request. What you basically are trying to figure out is what messages have arrived since a user has gone on vacation and what size those messages are. If you keep enough tracking logs (for the period a user is out), have advanced knowledge
of when a user will be out onb vacation and not checking their email. You could run something like this:
get-messagetrackinglog -start "2/14/2012 12:01AM" -end "2/24/2012 12:01 AM" -recipient <user on vacation email address> |ft totalbytes
This command would give you all list of the sizes of all the emails from 2/14/12 @ 12:01 AM til 2/24/12 @ 12:01 AM. You copy this to a excel spreadsheet and add all the columns up. Is that what you need? This may not be perfect as
there is no way to tell from that data when they last synched.. You would have to collate that data with something like this:
get-mailbox -identity <user on vacation email address> |ft displayname,WhenChangedUTC
Hope that helps.
JAUCG
