When you say Outlook, you mean Outlook.com?
N900 supports 'everything' outlook (software) supports. If the mailbox can be opened using IMAP or POP3, add it manually.

As indicated on my Wiki edit, Outlook.com should be added as an Activesync account, so you can add the mailbox via Mail for Exchange, in Settings/Connectivity. Contacts and Calendar sync also work flawlessly. It seems that different emails use different server names, but for me, s.outlook.com, port 443 works just fine.

Hope this helps.