While Roady [MVP] is correct on the big picture of Profiles, you can also use
a single profile to check many accounts (and send with the appropraite email
address of choice):
--Tools > Email Accounts
--"View or change existing e-mail acconts" & Next
--Click on Add... and add the apprpriate information per new account
--You can create rules to automatically move new messsages depending upon
account it come in via
Replying to a message should utilize the same email address it was sent to.
If startign a new message, you can use the "Accounts" button in the tool bar
to select with email address to act as the 'from' address. If that button is
not available, right click on the toolbar, shoose Customiae and you can find
the Accounts button in the Standad Categories list
Hope this helps