You can't switch accounts as in Outlook Express, but what you can do is have
multiple accounts and select which account you want to use to send and/or
receive as required.
Set up your accounts, then when you have composed your email, select
Accounts from the toolbar within the email and select which account you want
to send it from
When receiving, you can set your send/receive groups under Tools >
Send/Receive Settings.
You can receive from one account only or a group in Tools > Send/Receive and
select the account
Let us know how you go
Lee