I am using Windows Live Mail for years, but decided to use Thunderbird. I use my mail clients with POP3 connection. I can import my WLM messages into Thunderbird via Import Export Tools and imported all mesages into specified folder or hierarchical folders from WLM succesfully. But when I gets new messages from Server, occurs a problem for me. Thunderbird gets all messages even a message already imported from WLM. So all messages will be downloaded again and it will be seen twice in Inbox. But I want that a message was imported from local .eml/.mbox file, will not be download again. I imported messages both from eml and mbox file. (Used IMAPSize to convert *eml to mbox file) But there is no difference, Thunderbird still fetchs all messages. Windows Live Mail 2012 - Thunderbird 31.0 - Import Export Tools 3.0.1 - IMAPSize 0.3.7 ----- By the way there is a workaround for me, but I wish for finding a better solution. I can move all messages on server into a remote folder like archive or else. Or deleting all messages from remote inbox. Thus, Thunderbird will get new messages from a fresh inbox and my imported messages wil not be downloaded again.