Are the old and new accounts POP or IMAP? Is the old mail still on the mail server or just on a local computer? If it is on the server, does the new provider have the option to collect mail from another account, as does e.g. gmail?

Hi Thank you for replying both accounts are POP, I think the mail is on both the mail server and a my computer. As for whether if my new provider has the option to collect mail from another account, I don't know much about them, you might know more than me it is Virgin. If you need to know anything more please ask, I will answer as best I can.

If the mail is already on your computer, you could copy it to Local Folders to be available if you remove the old account. If you add the Virgin account to TB, the old mail in Local Folders is unaffected. If you were to, say, reply to an old message that was sent to the old address, you might have to switch the From: selection to the Virgin account, but I don't think there's any value in moving the old mail into the Virgin folders, especially if it's a POP setup. If you set it up as IMAP and needed to access the old mail from other devices, you could copy it from Local Folders to a Virgin IMAP folder, but only small amounts at a time.