So it's OK to take work-related email away with you? Is this on your own computer, or one at work and you want the messages at home? If it's your own computer, and it's using POP then you have all those messages on your own computer and they are yours to keep. You'll get irritating warnings about logins not working but the messages will be visible. You could then move them into your new account, or probably better, Local Folders in Thunderbird. If it's a work computer, and it's permitted to add other accounts, I'd create the new outlook.com account using an IMAP connection, and start copying messages I want to keep into it. Then those messages will be stored on the outlook.com server and accessible to you from home or wherever. However, you say it is a POP account and so all the messages are stored on your computer. In this case, assuming it's using Thunderbird, making a copy of your profile would result in a copy of all your messages (and much else) that you can take with you. You could set up thunderbird to work with the old profile, or import selected folders. In this case, the imported messages would initially be placed in Local Folders and that may well be enough. If you need to have them more universally accessible, you can, again, move or copy them into your new working account. For copying a profile see: https://support.mozilla.org/en-US/kb/profiles-tb If your POP-based account is being serviced via another email client, then you need to seek advice on how to extract data from it from its own help sources.