"Who From" setting for multiple internet accounts

[Guest]

Greetings!

Can anyone solve the problem on how to switch who a
composed email is from, when using multiple internet
accounts?

I receive email fine for both, but when I click on "New"
message, I cannot seem to figure how to make the "From:"
indicate my preference for which of the two internet
accounts I want the message to be from.

For example, I'm sending an email to clients from company
B, but the "From:" box in the header always shows the
email as coming from company A. Is there a way I can
chose whether the new message is coming from company A,
or from company B?

If you know the answer, please send to:
(e-mail address removed)

Thanks!

Mark Mays