When I get an email sometimes I only need to keep it for a few days or
weeks. By the time it is out of date it has disappeared down my
inbox, so it often does not get deleted.
When I get an email is it possible to put on a setting to delete it on
a date in the future? I could put on a flag to remind me to deletion
later, but would like it even better if it deleted without any further
input.

Not exactly.

What you could do is this.

Create a few subfolders under your Inbox, one called Keep for a Week, one
called Keep for a Day, one called Keep for a Month, one called Keep Permanently.

Set up the Autoarchive settings on each of those subfolders to remove messages
(whether you archive or permanently delete) after the obvious period of time.

Set up a Search Folder (I'm going to assume you're running 2003 or greater
since you didn't bother to say) that basically will return all messages from
the Inbox and below.

Use the Search Folder, rather than the Inbox, for generic viewing of mail.

Move the message to whichever folder after reading.

Well, ok, after checking, if you pull up the options of a message, there
is a Message Expiry setting that it looks like you can set on a message and
it seems to work. I still kinda like my solution, but either works pretty
well. My solution works better if you want to archive the message and not
delete it.

--
-f.h.