Free
Free OST to PST converter for Outlook. Retains the original structure.
Free and fast Outlook OST to MBOX converter. Retains the original structure.
PC-to-PC Communication Software Suite
Free OST to MSG converter for Outlook. Retains the original folder structure.
Free Outlook email message converter from OST files to EML format.
Imports OST files into Outlook: Office 365, Exchange Server, Gmail, and others.
Free tool for importing Outlook Master Category List from XML file.
Imports Outlook notes from text files retaining the original folder structure.
Imports appointments and meetings from MSG files to Outlook calendar folders.