Then start the New Account process, and after you enter your email address, you'll be presented with a "Configure manually" option where you can enter the server information you gathered.

If it's a well-known email provider, Thunderbird may know the proper server settings based on your email address, and do a good basic job of setting it up for you. You will be prompted through this when you first install Thunderbird. After that, go to <Account Settings> and click the "New Account" button. If this is a less well-know provider or the automatic process fails, gather the correct settings from their support web site. You will need to know: for incoming: Protocol (IMAP, in this case) Hostname/server name Port Connection security (STARTTLS or SSL/TLS) Authentication method (usually Normal Password or OAuth2) Same info needed for the outgoing (SMTP) server. Then start the New Account process, and after you enter your email address, you'll be presented with a "Configure manually" option where you can enter the server information you gathered.