No More Identities
In Outlook Express you’d need to create a different identity if you wanted to separate your email addresses completely from each other – otherwise you’d need to create separate folders and filters. With Thunderbird, you can choose not to store your email messages in the local folder and a new folder will automatically be created with the name you choose during its creation.
This makes it easier to customize when and how each individual email address is checked and you don’t have to worry about mixing all your messages in just one inbox.
NOTE: the order that you enter the accounts into Thunderbird will be the order the folders appear in the sidebar. The very first email address you enter will become your default. However, there is an extension which lets you work around this.