You may want to remove an email account from Mail, for example if you no longer use the account.
Important: Removing an account will permanently delete its mailboxes, messages, notes, and to do items. If you want to keep those, be sure to copy them to an On My Mac mailbox before deleting the account.
Exchange, IMAP, and MobileMe accounts store their mailboxes and messages on the server; deleting these account types in Mail will not permanently delete messages from the server. However, if you are not completely certain that your account is one of those types, be sure to copy the mailboxes and messages you want to keep into an On My Mac mailbox, or save individual messages manually by selecting them and choosing Save As from the File menu.
To remove an email account in Mail:
1) Open Mail (click it on the Dock or open it from the Applications folder).
2) From the Mail menu, choose Preferences..., or press Command-, (the Command and comma keys).
3) Click the "Accounts" icon.
4) Select the account you wish to remove.
5) Click the "-" (minus) icon. You will be alerted that "The account's setup information, mailboxes, messages, notes, and to do's will be deleted permanently from your computer."
6) If you are sure you want to remove the account and email messages from your computer, click "Remove" to complete this process.