It's not exactly based off the received date or the date on the email. It actually follows a "ChangedDate" thats internal and gets updated based on various actions against the email. 

There's another optimization I'm thinking of but I don't remember if we implemented it. Keeping the top/last ~50 items in the folder on primary. Though it's very likely the first scenario given the size you indicated.

Thanks, Matt.  Would it be possible to off-load emails based upon their actual age?  I may be in the minority when I say that is the behavior I expected.  Especially when I am on-boarding new customers with a couple hundred GB of emails imported via Outlook/IMAP or, as will happen later today, Exchange migration.

I think there were some strong technical reasons for why we are doing it using the changed time. That way their clients and webmail remain snappy for new (or recent moved, etc) messages and we don't put a huge load on secondary storage which are very likely slower-storage mediums. There could be changes to how we do this or how we treat imported messages to maybe help these specific scenarios. 

In my environment, there is no difference between primary and secondary storage, so performance at this level is not an issue.  Right now, the constraint is storage provisioning.  That said, I suppose I could cheat it a bit to get things to move: right now, I have the division set at 365 days, but if I halve that, if things work the way I think, the move could be triggered for almost all of the affected domains.

Does the move depend upon filesystem access times of the data?

Thanks for the info.  Not exactly what I was expecting, but I can work with it.