These directions are written to use Outlook 2003. These are generic instructions, written for a fictional company "XYZ", who owns the domain name "domain.xyz", and hosts their email on my "secure.jms1.net". server
The first time you run Outlook, it will try to walk through an automatic "transfer settings" procedure. When this happens (i.e. when it asks about importing settings from other programs, press Cancel.
Pull down the "Tools" menu and select "E-mail Accounts..."
Choose the "Add a new e-mail account" option.
Click the Next > button.
Select IMAP as the server type.
Click the Next > button.
For "Your Name", enter your name as you wish it to appear on your outoging email.
For "E-mail Address", enter your full email address, ending with "@domain.xyz".
For both "Incoming mail server (IMAP)" and "Outgoing mail server (SMTP)", enter "secure.jms1.net".
For "User Name", enter your full email address, ending with "@domain.xyz".
If you want Outlook to remember your mailbox password, enter it in the "Password" field, and turn on the "Remember pasword" checkbox.
Make sure the "Log on using Secure Password Authentication (SPA)" checkbox is turned OFF.
Click the More Settings... button.
You can change the account name if you like- this is the name which Outlook uses to refer to this account, and does not have to have any specific setting in order to work with the server.
Click on the "Outgoing Server" tab (at the top of the window.)
Make sure the "My outgoing server (SMTP) requires authentication" checkbox is turned ON.
Make sure the "Use same settings as my incoming mail server" option is selected.
Click on the "Connection" tab (at the top of the window.)
Outlook has the ability to make your computer dial out to reach the Internet, if you use a dial-up connection. My experience with this is that it's a nice idea, but it doesn't work very well. I recommend you set this to "Connect using my local area network (LAN)" regardless, and if you are using a dial-up connection, make sure to connect to the Internet before you run Outlook.
Click on the "Advanced" tab (at the top of the window.)
Under "Incoming server (IMAP)", turn ON the "This server requires an encrypted connection (SSL)" checkbox. When you turn this on, you should see the port number automatically change from 143 to 993. If not, change the IMAP port number to 993 by hand.
Under "Ourgoing server (SMTP)", turn ON the "This server requires an encrypted connection (SSL)" checkbox. When you turn this on, you should see the port number automatically change from 25 to 465. If not, change the IMAP port number to 465 by hand.
Click the OK button.
Back on the "Internet E-mail Settings (IMAP)" window, click the Next > button.
The mailbox is now configured.
Click the Finish button.
The first time Outlook connects to the server, it will show this warning about the security certificate. This is because the SSL certificate which handles the encryption for the IMAP connection is self-signed, rather than being signed by an external "certification authority".
Click the Yes button.
Once Outlook has connected to the server for the first time, you will see any server-side folders as "children" of the "Inbox" folder. By default, you will have folders called "Drafts", "Sent", and "Trash". DO NOT delete these three folders- they are used by Outlook and other IMAP clients, including the webmail interface.
You can create folders as children of the "Inbox" folder in the new account. Those folders are physically stored on the mail server, which means they will be accessible through any other IMAP client, including the webmail interface. The contents of these folders will also be backed up on a regular basis.
You can also create folders as children of the "Outlook Today" item. However, those folders are physically stored on your hard drive and will not be accessible from any computer other than the machine where you're running Thunderbird. In addition, these folders will probably not be backed up, so if something happens to your desktop computer, anything in those folders is gone.