Mail, confiiguration, problem with interface

Simplest one first. When on the home page under RT at a glance and 10
highest priority tickets I own, the ticket # goes to the ticket but the
ticket subject goes to 404 not found. The problem is the location should be but it is going to I’ve been through all the
configuration and double checked the setup and can’t find a problem. The
suject doesn’t do this under the tickets with no owners on the home page.

Mail configuration. I run a mail server with SMTP, POP, IMAP, etc. RT is
sending mail using it’s own SMTP sender. It gets to my mail server and
accepts the emails because it’s from a trusted IP address. Emails going to
other domains, though, are not making it to their destinations. They are
being blocked because they are not originating from my mail server. Is
there a way to get the emails from RT to send through my mail server? I use
SMTP authentication. Also, how does RT retrieve the emails? I do not see
where I would enter a server, username, and password for retrieving emails.

General configuration setup. I was hoping someone could help with this. My
company supports multiple clients. We want our support staff to have full
control over all tickets submitted. Each client will have one or more
administrators who can run reports, view and reply to all tickets submitted
within their company, but not see comments or edit fields like owner. They
can also watch tickets and submit new ones. The clients will also have
multiple users who can only see tickets they created and reply to them. How
would I go about setting this up? Use queues for each company?

Hosted service. Would I need to run another instance of RT to be a
“hosting” service for local companies? If a company wants to have their own
RT but doesn’t want to setup a server to do so, can I use my existing RT to
do so?

Thanks a bunch for any help!