From MozillaZine Knowledge Base
Account Settings is a dialog where you can configure settings for your accounts.
You can open Account Settings in three ways:
Account Settings always shows settings for all your accounts, including Local Folders, no matter which account you open it from.
At the bottom, below all your accounts, it has settings for your outgoing (SMTP) mail servers.
For information about the relationships between accounts, servers and identities, see: Mail concepts
Settings for each account
Account Settings has various pages of settings for each account, depending on the type of account. Some of the settings are server settings, relating to incoming mail from the account's server. The other settings are identity settings, relating to your identities for outgoing mail. Unfortunately, the server settings and identity settings are mixed together in a confusing way.
The Account Name setting on the account's main page is only for your information. Thunderbird does not use it for any other purpose.
Settings on the following pages relate to the account's server for incoming messages:
Settings on the following pages relate to the account's default identity for outgoing messages:
To work with settings for all the account's identities, press the Manage Identities button on the account's main page. To change an identity's settings, select it in the list and press the Edit... button to see the Identity Settings dialog.
The top identity in the list is the account's default identity. Its settings are duplicated, appearing both in Account Settings and in its Identity settings dialog.
For more information, see: Multiple identities per e-mail account
Note: Security settings are not available in the Identity Settings dialog. For more information about this bug, see: Installing an SMIME certificate
Outgoing Server (SMTP) settings
Use the Outgoing Server (SMTP) page to work with the master list of SMTP servers.
For more information, see: Multiple_SMTP_servers_-_Thunderbird
Settings in Account Settings are stored as preferences. For information about other ways to work with them, see: Editing configuration
In the preferences, each account, server and identity has a number. You can identify various types of preference by looking for the following prefixes: