Catch Up marks all messages as Read, even those not downloaded from the
server. From OE's Help:

To mark messages as read

a.. To mark an individual message as read or unread, select the message.
On the Edit menu, click Mark as Read or Mark as Unread.
b.. To mark all newsgroup messages as read when you quit Outlook Express
or go to another newsgroup, on the Tools menu, click Options. On the Read
tab, select Mark all messages as read when exiting a newsgroup.
c.. To mark all messages in a selected newsgroup as read, including
messages not yet downloaded, select the newsgroup in the Folders list. On
the Edit menu, click Catch Up.
This is handy, for example, when you return from vacation and don't want
to download all unread messages, but want to start reading the current ones.

d.. To mark all the messages in a given newsgroup conversation as read,
select either the original message or any of its replies. On the Edit menu,
click Mark Conversation as Read.
A conversation is an original message and all its posted replies.
Conversations are sorted and grouped according to the title of the original
message. For example, a conversation that starts with a message titled
"Ideas for Labrador owners" includes all of the replies, titled " Ideas
for Labrador owners."

Note

a.. E-mail and newsgroup messages are automatically marked as read after
they are open for a certain length of time. If you don't want messages
automatically marked, on the Tools menu, click Options, click the Read tab,
and then clear the Mark message read after displaying for x seconds(s) check
box.
****************************

The way to undo all of this is to uncheck: Get XXX Headers at A time. Then:
Tools | Options | Maintenance | Clean Up Now. Select the group, or server at
the top and then Reset.

When all is done, follow up with a compact all folders.

Click on Outlook Express at the top of the folder tree so no folders are
open. Then: File | Work Offline (or double click Working Online in the
Status Bar). File | Folder | Compact all folders. Don't touch anything until
the compacting is completed.
--
Bruce Hagen
MS-MVP Outlook Express
Imperial Beach, CA


"Boze" wrote in message
...
I'm setting up my newsgroups on a new computer. I chose 'CatchUp' without
knowing what it REALLY did. Now when I try to download more messages I
only get new messages, can't get any older ones.
For future reference, what did I do? And is there a way to UN-do the
Catch-Up after I selected it?
Thanks in advance
Boze