From MozillaZine Knowledge Base

Beginning with version 0.8, Thunderbird now has a Global Inbox feature that allows you to have your mail from multiple POP accounts go into a single Inbox, in Local Folders. You can choose to have all or only some of your POP accounts use the Global Inbox, as you wish. Each account that does not use the Global Inbox will have its own set of folders, including its own Inbox, displayed in the folders pane. Accounts that do use the Global Inbox will not have their own folders displayed in the folders pane; instead, all you will see is the single set of folders in Local Folders.

When creating a new account

When you create a new POP mail account in Thunderbird, the Account Wizard will ask if you want to use the Global Inbox for that account. If you do, then make sure that the box for this feature is checked. If you don't, then make sure the box is unchecked.

If you often create new accounts, you can set the default in the Account Wizard by setting the preference mail.accountwizard.deferstorage to true (to check the box by default), or false (to clear the box by default). In a new Thunderbird profile this preference does not exist initially, so you must create it as a new Boolean preference.

Changing the Global Inbox setting for an existing account

To change the Global Inbox setting for an existing account, you need to follow three simple steps.

Change the destination Inbox

Go to "Tools -> Account Settings -> Server Settings" and click on the "Advanced" button. A dialog box will then pop open.

To set the account to use the Global Inbox, select "Global Inbox (Local Folders Account)" and click "OK".

Important: if the account already has messages in the Inbox or other folders, you should copy or move these messages into Local Folders before setting the account to use the Global Inbox. If you don't copy or move the messages into Local Folders and you set the account to use the Global Inbox, the account will no longer be displayed in the folders pane and you will not be able to access those messages unless you go back and undo the Global Inbox setting.

To set the account to not use the Global Inbox, select either "Inbox for this server's account" or "Inbox for different account" and click "OK".

Check settings for other folders and filters

After you have changed the account's setting for which Inbox to use, see if any of the following need to be changed:

• Go to "Tools -> Account Settings -> Copies & Folders", and look at the destination folders for Sent, Drafts, and Templates. Make sure that the messages for each will be stored in your preferred folder locations.
• If you are using junk-mail filtering for the account, go to "Tools -> Account Settings -> Junk Settings" and verify that the folder selected for Junk messages is the one you want to use.
• If you have set up any filters, go to "Tools -> Message Filters" and make sure that they will work properly with your new Inbox configuration. Especially important if you are changing an account so that it will start using the Global Inbox: if you have set up any filters that sort messages into any of the folders for the account, you should disable/delete those filters or change the destination folders.

Exit and restart Thunderbird

Important: exit Thunderbird and restart before downloading mail into any account whose Inbox/Global Inbox setting you've changed. If you do not exit and restart, messages might continue to download into their "old" locations (e.g., into the individual account Inbox rather than the Global Inbox).

How to identify what messages are from which account

The easiest way to identify what account (mailbox) you recieved a message in is to use seperate accounts in Thunderbird. However, you could:

• Add the Recipient and/or the Account column to the window listing the messages in a folder by clicking on the little icon at the right end of the column header. However, the Recipient column can be empty if the To/CC header was empty or you were BCC'd, it could have "recipient list not shown:", and the Account column is blank in IMAP accounts.
• Use message filters to automatically assign a different colored label to new messages from each account.
• Use message filters to automatically move new messages for each account to a separate child folder in the global inbox.
• Use saved searches to create a seperate folder for each account. This is a virtual folder so the messages would still be stored in the global inbox. You could switch between the global inbox and the searched search folders at will, depending upon how you want to view your messages.

Other information

• Accounts that use the Global Inbox are sometimes called "deferred" accounts, and it is possible to create deferred accounts that do not use Local Folders for the Global Inbox. For example, if you have three Gmail accounts, you could set up two of them to store their mail together with the mail for the other Gmail account but outside of Local Folders. To do so, follow the procedure above for setting the destination Inbox, but instead of selecting "Global Inbox (Local Folders Account)", select "Inbox for a different account" and then from the dropdown list choose the account you want to use.
• For deferred accounts, if you go to "Tools -> Account Settings... -> [account name] Server Settings", you will see that "Local directory" does not point to the actual location in your profile folder where the mail is stored. This is normal and necessary because certain files for each deferred account need to be stored separately from the shared mail files. (For instance, each POP3 account has its own file called "popstate.dat" that keeps track of which messages have been downloaded from the server. Account-specific message filters are likewise stored in a separate folder for each account.)
• If you want to use message aging with a deferred account, note that no settings for the retention policy are provided in the "Disk Space" settings of that account itself. Instead, the retention policy applies where the Global Inbox is located.

Alternative approach (Advanced)

A global inbox is a useful way to create a common inbox for several accounts, but it also hides the existence of those accounts in the folder pane. If you don't want to hide those accounts you could create a common inbox using saved search instead. It creates a virtual folder made up of whatever folders you specify. The messages would still be stored in each accounts inbox folder, it merely provides a way to view them as if they're all in one folder. The name is slightly misleading as it implies its a snapshot - any changes in the inbox folders also occur in the virtual folder.

You could use File -> New -> Saved Search to do that:

• Select the inbox folders using the "Choose" button
• Set "create as a subfolder of" to "Local Folders"
• Type "Global Inbox" as the name
• Click on "match all messages" as the search criteria (at the bottom of the window)
• Press the OK button

Smart Folders (Advanced)

Nightly builds of Shredder, the unreleased next version of Thunderbird 3, has an additional choice in the advanced folder views called Smart Folders. It creates what looks like an Inbox account that transparently merges the contents of all the inbox folders (both POP, IMAP and local folders). It moves the inbox from each account to a child folder in the Inbox account. Any messages in an inbox show up in both the root of the Inbox account plus the child folder for that account.

Each account still displays any child folders of the inbox, only its inbox folder was "moved". However, Shredder doesn't actually change where/how the messages are stored, its just another way to view your folders, similar to what you can do with a saved search (a type of virtual folder).

See Testing pre-release versions if you are interested in running Shredder. Beta builds are available from the Mozilla Messaging web site. Beta 3 added support for Smart Folders.

Its recommended you don't share profiles if you want to check out Shredder. However, if you do that don't select Smart Folders in Shredder. That will create a "Smart Folders" account in Thunderbird 2 the next time you run it. Unfortunately its not harmless, it occasionally displays duplicate messages or message fragments that don't exist in various accounts folders. They go away if you rebuild the index. You can't remove the Smart Folders account using Tools -> Account Settings. You need to either edit prefs.js with a text editor or use the Config editor to delete the account from mail.accountmanager.accounts.