Thunderbird creates a Profile folder to hold mail accounts. You can have one or more Profiles. You can have many mail accounts in a single Profile. A mail account is for an email address. A mail account can also have more than one 'identity', this can be used for certain circumstances. see info on 'identities; http://kb.mozillazine.org/Mozilla_Suite_:_FAQs_:_Mail_Aliases So assuming you really mean 'identity': The default identity mail account will be listed in the left Folder Pane. All incoming mail from all of the mail account 'identites' will be shown in the folder(s) you specified, usually they are set up to be in the same Inbox etc. So you do not need to swap identites to see the emails as they are all together. Hence, why I'm unsure that you are using the correct term - we may not be talking about the same thing. When you want to Write a new messge using a specific identity, you select it from the FROM drop down list. If you wan to swap the default identity: Tools > Account Settings for the mail account click on 'Manage Identites' select the identity and click on 'Set default' click on 'close' click on OK to save changes.