Although Outlook uses many Standard Windows Shortcuts this page consists of shortcuts (mostly) unique to Outlook.

Address messages quickly with Ctrl+K

Unless using auto-correct (Outlook XP and later) the easiest way to quickly address an email message is to type the first name, last name or email alias of any user then press Ctrl+K. Before pressing Ctrl+K, multiple entries can be entered, separated by semicolons. Ctrl+K means "Check Names". It really means: Compare what you've typed against the Global Address List (GAL); if it finds a unique match, resolve (complete) the address. If it finds two or more matches you'll be given a list to pick from. If Outlook finds no matches, it proceeds to the Contacts and does the same.

It is possible to switch the lookup order so that Outlook first looks to resolve addresses against Contacts and then looks to GAL* second, if not found in Contacts. This is especially helpful if you send lots of mail outside your organization.

*The lookup in GAL only happens if you're using Exchange; essentially, a network installation of Outlook.