archive email - .pst replacement

I have a strategic question. If we were to transfer to Zoho Business, how would the archiving of emails work?

right now we have a 250 mb limit on the MS Exchange for email, but we are also required by law to save all of our emails. To archive them, we drag them off the Exchange server into .pst files in Outlook. Currently I have about 3 GB of archived emails and that number grows every day.

Do you have a plan for allowing users to archive emails? Is it possible to create a .pst file type system that can archive emails on the local hard drive and integrate with Zoho mail at the same time?

If not, do you plan on offering inexpensive additional space like Gmail does (I think Google charges $25 per year for 6 GB).

Thanks,

James