First off, Windows Mail is Free versus Outlook which must be Paid For.
Outlook is a much more powerful program with many more features.
If a simple mail program is sufficient for you, use Windows Mail or one of
the other free alternatives available (like Thunderbird)..
If you need multiple identities/accounts, Outlook is a better choice.
They are almost completely different. Windows Mail is an E-mail client
and newsreader. ms Outlook is a personal information manager that also
does E-mail. They overlap in one relatively small area--they both do
E-mail.