You just set up all your email accounts on both machines. Ideally, you would use IMAP, where the messages are stored on the server and so both machines same the same set of folders and messages. If your email provider doesn't offer IMAP, then I'd suggest you find one that does. All the well-known free email systems offer IMAP. If your email provider only offers the older POP service and you're totally unwilling to switch away from this provider, then the best you can do is to set each Thunderbird to leave messages on the server. That way you will at least see any incoming new email on either machine Or, you can set up a new IMAP-connected account with, for example, gmail or gmx, and set your preferred account (at the server!) to forward its messages to the new IMAP-connected account. Both of these services (gmx and gmail) allow you to register a "foreign" email address and handle it so your messages appear to be from/to your old preferred POP-based address. Other services (e.g. yahoo, outlook, aol) may have similar features.