Express does not have, such as a calendar,
a task list, a journal, and automatic backup into
archive files.
Outlook also has a very powerful Junk Mail feature.
Outlook has message rules for both incoming
and outgoing mail, while Outlook Express can
only filter incoming.
Outlook Express was designed for use on a single
computer and so its message store and settings
cannot be stored on a server. Outlook however
was tailor-made for networks, and so its message
store can be on a central server that many
machines can access.