Presumptions:
- You have an IMAP mail account on one server, and you want to migrate this account and the messages to another server.
- The old server is still up and running and the nameservers point to the new hosting (e.g. the server you are migrating the messages to)
OK, here goes:
1. Create a mail account in Thunderbird using the new server credentials.
2. Ensure the account is setup as IMAP in Thunderbird – a world of pain ensues if you neglect this step!
3. Let Thunderbird connect and test the email settings are correct.
4. Send a test email (to anyone at all) so that Thunderbird creates a sent messages folder.
5. Deselect any default Junk mail options for the account (this will stop Thunderbird automatically shifting some of the mail into different mail boxes).
6. Now go to the mail server settings for your old account. You will need to replace the old incoming and outgoing mail server settings (which will probably be mail.yourdmainname.co.nz) with the IP address of the old server.
7. Once Thunderbird has connected again to the old email server you will need to make folders in the new mail account that mirror the ones on the old servers account.
8. In the old Mail account (the one you are migrating from), select each mail folder, CTRL+A to select all the messages, right click and choose ‘Move to…’ and select the equivalent folder on the NEW server version of the account.
9. Repeat step 8 for all folders/messages in the account (don’t forget the Sent items!).
10. Repeat entire process for every mail account you need to migrate.
Once all your sent and received messages have been copied across to the new email account, you can delete the old account.