Gnus IMAP Qs: catch-up vs delete vs expire & "gnus-expire" tag ?

[David Masterson <dsmasterson@gmail.com>]

I have a number of questions...

I've been trying to set up my mailing list environment using Gnus with
IMAP/SMTP via zohomail.com.  I can read gnu.org mailing lists via IMAP fine.

1. SMTP thru zohomail.com to gnu.org gets bounced as "Undeliverable" due to
a "550 - bad domain" error.  Zoho support says the email looks fine.  I've
been trying to get an answer from sysadmin@fsf.org (email sent from my
gmail account) for several days, but no reply.  Anyone seen anything like
this?

2. Due to limited space in a free account on zohomail.com, I want to clean
up old mail on both my system and the server.  I assumed the way to do
that was (mostly) by "catchup", but that just marks all the mails in the
summary buffer as read.  How do you delete old email?

3. I thought 'expire' was the way to delete, but the manual implies that
expired email can be deleted by Gnus at some future time.  How is that
controlled?

4. I found that the expired email wound up being tagged with "gnus-expire"
on the IMAP server.  Is there an assumption that the IMAP server will
delete emails tagged with "gnus-expire"?  If so, how does that work?

5. Is this documented in the Gnus manual?  At least the assumptions of how
the IMAP server should work around "deleting emails".

--
David Masterson
Programmer at Large