Thunderbird is the email client - a program running on your computer. It has 'mail accounts' for email addresses. Emails are sent to the email address and are received by the server. Thunderbird downloads emails from that server for that email address.

You can forward emails from one email address to another, but this is best done by sending from one server to another. Logon to your webmail account using a browser to use server settings to do this.

1. but does this automatically forward future mails sent to the old email address to the new one?

2. i thought of setting the "reply to address" in the old mail account to be the new email address. Would that work?

1. but does this automatically forward future mails sent to the old email address to the new one? It would auto send emails received on old address to new address, but sender is still using old address to send emails.

2. i thought of setting the "reply to address" in the old mail account to be the new email address. Would that work? Yes, this would be a good idea. It may also help you to advise recipients to update their records to replace stored email address in their contacts with the 'Reply-to' email address. This may eventually get everyone using the new address.