Você pode importar as mensagens para o Outlook Express e salvá-las como arquivos EML ou usar o Extrato do Outlook
OutlookExtract is a tool that helps you to extract your e-mail messages and Attachments contained in MS Outlook, Outlook Express and Windows Mail. You can save the messages as Mime (.eml), Outlook message (.msg), Adobe PDF or as Text / Html Files.
Outra opção:
Just double click on the message, go up to Save -> Save As and under the file type choose Text .txt .
This is the same as EML format, you can just change the file extension from .txt to .eml