Under the Help Menu, you can find the Migration Assistant to help you set up Thunderbird the way you want it. If you liked the old toolbar from Thunderbird 2, you can quickly make that change with the Migration Assistant. You can also install add-ons from the Migration Assistant like Advanced Folder Columns and Compact Header for your message display window.
Mail Account Setup Wizard
Prior to this feature you had to know your IMAP, SMTP, and SSL/TLS settings. Now all you need to provide is your name, email address, and password and the email account set up wizardry will check our database and find the email settings for you.
One-click Address Book
One-click Address Book is a quick and easy way to add people to your address book. Add people by simply clicking on the star icon in the message you receive. Two clicks and you can add more details like a photo, birthday, and other contact information.
The attachment reminder looks for the word attachment(and other words like file types) in the body of your message and reminds you to add an attachment before hitting send.
The Activity Manager records all the interactions between Thunderbird and your email provider in one place. There's no more guess work. You only have to look in one place to see everything that's happening with your email.
Quick Filter Toolbar
The Quick Filter Toolbar lets you filter your email faster. Start typing in words in the Quick Filter search box and the results are displayed instantly. Or you can filter your email by New Messages, Tags, and people in your Address Book.
You can also "Pin" or save a Filter and use it across multiple folders.
If you like Firefox's tabbed browsing, you're going to love tabbed email. Tabbed email lets you load emails in separate tabs so you can quickly jump between them. Perhaps you're responding to an email and need to refer back to an earlier email. Tabbed email lets you keep multiple emails open for easy reference.
Double-clicking or hitting enter on a mail message will now open that message in a new tab window. Right-clicking on messages or folders will open them in a tab in the background.
When quitting Thunderbird, visible tabs will be saved and will be restored when you open Thunderbird the next time.
There is also a Tab menu on the Tab toolbar to help you switch between Tabs.
The search interface in Thunderbird contains filtering and timeline tools to pinpoint the exact email you're looking for. Thunderbird also indexes all of your emails to help you search even faster. Your search results are displayed in a tab so you can easily switch back and forth to your search results and other email.
If you think you're going to need an email in the future but want it out of your inbox without deleting it, archive it! Archiving helps you manage your inbox and put your email into the archive folder system.
Selecting the Archive button or hitting the 'A" key will archive your email.