Applies to Outlook 2013:

With a Microsoft Exchange Server account or Office 365, you decide how many items are available when working offline.

When GeniusConnect synchronize database records (old mails etc..) to an Outlook folder and the record datetime exceeds your "Keep offline" setting, Outlook will delete these items!

Please set "Mail to keep offline" to "All"


http://office.microsoft....offline-HA102821311.aspx 

Another option is to set a filter (Assign Table Dialog->Filter Rows) to sync only subset of your DB records .