• Sharing a mail folder (or calendar) allows someone access to that folder. You specify the level of access, from read-only up through full create/edit/delete privileges.
• Delegate access lets someone act "on behalf of" you. When you grant delegate access, messages or calendar event invitations will come from an address in this format: Arnie Assistant on behalf of Mary Manager. You can grant Delegate access with any level of sharing (or with no sharing at all).
• Send As rights allow someone to send messages, replies, and calendar event invitations in the persona of that person. This is most commonly used with Group Accounts. For example, Arnie Assistant could send a message that comes from "Limnology Department Mailbox" rather than his own email address.

Delegate Access & Sharing for Outlook on the Web

Full, writable delegate access control is not currently supported in Outlook on the Web. Ideally, delegate access should first be set up using with an Outlook client using the above instructions. Once an Exchange user has delegate access to an account, the user receives read-only access to the mailbox through Outlook on the Web.

While full access control is not available, it is possible to share a calendar (as Read Only) when using Outlook on the Web. Note, however, that calendar permissions that have been customized using the Outlook client cannot then be changed using Outlook on the Web.