If are you looking best tool for importing PST files to Office 365 you can try this Aryson PST File Converter Tool. This tool is the most efficient tool for importing PST files to Office 365 and many more email clients such as Outlook PST email to Thunderbird, Gmail, IMAP, Hotmail, Yahoo, & Opera Mail successfully. It also can convert PST, to EML, PDF, TXT, MSG, MBOX, HTML, EMLX, MHTML, etc., file formats with ease. It maintains the folder hierarchy during conversion as per the browse PST file structure.