Gnus header re-scan

[ross@rosslaird.info (Ross A. Laird)]

This is probably in the gnus docs, but I usually find it difficult to
find what I need there, so I thought I'd ask here:

Often I need to go into an archive directory to find old email or
addresses. In mutt, once the headers are downloaded, subsequent rescans
of the archive are very fast (the archive has about 15,000 messages in
it). But gnus seems to want to re-download all the headers again (with
C-u space, for example), and this can take as long as 10 or 20 minutes.
Can I get gnus to work like mutt in this regard, by looking at the local
copies instead?

Also, gnus does seem to have trouble with my imap server. It sometimes
says there are no new emails, when in fact there are. But that's another
issue.

Thanks.

Ross

-- 
Ross A. Laird, PhD
www.rosslaird.info