From defaults to Contact Name, turn off?

[James]

Hi... I have outlook connected to out exchange server. I have several emails
setup
i.e.
(e-mail address removed) (default)
(e-mail address removed)
(e-mail address removed)
(e-mail address removed)

all under the same user in the servers Active Directory.
When I want to send an email from (e-mail address removed), I type it into the
from box, however this automatically changes to Name SecondName... Which
results in the receiver of the email seeing (e-mail address removed) (default email)
as the email it was sent from...
(Hope you're still following!)

My question is, how do I turn this off, or get around it so I may send
emails from the several different email addresses under the same user.

Hope that all made sense!
Thanks in advance.