Where is the return email address stored -- the one Outlook uses as
the "Sent from" address when I send email out?

Can I create two such return addresses?

I have a case management program (Time Matters) that uses Outlook to
manage email. I would like all email sent from TM to have my business
return address ("mail@xxx") rather than my personal email address
("myname@yyy").

I am told by the tech that there is no way to change the "Sent from"
email address in TM, because it uses whatever is set up in Outlook. I
thought that if I could set up a second one in Outlook, I might be
able to get one of them to use a different one.

Thanks for any suggestions or pointers.