From MozillaZine Knowledge Base

Thunderbird has a optional Global Inbox feature that stores mail from multiple POP accounts in a single Inbox in Local Folders. You can have all, some or none of your POP accounts use the Global Inbox. 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 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.

See Virtual Folder and Unified Folders for some alternatives. They will work with both POP and IMAP accounts.

When creating a new account

When you create a new POP mail account in Thunderbird, the Account Wizard may ask if you want to use the Global Inbox for that account. If it does that (and you want a global inbox), check that feature. If it doesn't ask (recent versions don't) then you need to select "Global Inbox (Local Folders account)" in Tools -> Account Settings -> Server Settings -> Advanced. Try to do that before Thunderbird checks for new mail to avoid complications.

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 received a message in is to use separate 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 tag to new messages from each account or automatically move new messages for each account to a separate child folder in the global inbox.
• Use the Account Colors add-on to to highlight mail using a separate color for each identity (email address).
• Use saved searches to create a separate 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.

Alternative solutions

Virtual Folder

Saved Searches can be created to combine the inbox folders (or any folder) of several accounts, to give the appearance of something like a global (inbox) folder. Each account's inbox will still be visible in the folder pane and still physically stores the messages, but you can manipulate messages in the virtual folder just as you can do in the physical folder. A virtual folder can include folders from both POP and IMAP accounts, and even a (real) global inbox. You can use File -> New -> Saved Search to create, and :

• Select the inbox folders using the "Choose" button
• Set "create as a subfolder of" to "Local Folders" (or some other folder)
• Give it a name (probably not wise to call it Global Inbox - doing so may cause confusion with a "real", Thunderbird-created Global Inbox)
• Click on "match all messages" as the search criteria (at the bottom of the window)
• Press the OK button

Unified Folders

Unified Folders (originally named Smart Folders when it was added in 3.0) is a folder pane view which looks like a global inbox account by merging the contents of all inbox folders (both POP, IMAP and local folders) from all accounts. It also shows the inbox of each account as a child folder of the unified Inbox account. Any messages in an inbox shows up in both the root of the unified Inbox, plus the child folder of the unified Inbox for that account.

Each account still displays any child folders of the inbox, only its inbox folder has been "moved" away from the account. This does not, however, change where and how messages are stored. In other words, Unified is just another way to view your folders, similar to what you can do with a saved search (a type of virtual folder).

Use View -> Folders -> Unified Folders to select it. If you don't want to use it, use View -> Folders -> All Folders to select a more traditional display. Thunderbird 10 eliminated the ◄► arrows at the top of the folder pane that you could use to cycle between different views.

Use message filters to create a single inbox

You could create a message filter in each account that automatically moves any new mail to the inbox in Local Folders. That would work with both POP and IMAP accounts. The main limitations is that it is not useful if you get new messages in other folders in an IMAP account.

Replace several accounts with one account (Advanced)

Some email providers provide free email accounts that can periodically automatically fetch mail from other POP servers and store it in their inbox. Gmail, Gmx, Fastmail, and Windows Live Hotmail support that for example. Its possible to replace all of your accounts with a single account in Thunderbird, using that feature plus multiple identities. This is not hiding the other accounts like a global inbox, you literally only have one account in Thunderbird.

See Replace several accounts with one account for more information.

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.