There are many tools but I have found EmailsGuru EML to PST Converter, most easy to use and reliable. It is dedicated tool to import emails from EML to Outlook PST format. After using this tool, users don’t need to use Outlook. It is capable to convert multiple EML files to PST at once. This tool is fully compatible with many EML supported email applications like Windows Live Mail, Outlook Express, Mozilla Thunderbird and many others. It is Windows based tool, offering new users a free trial version.