[horde] what are the relationship of user authentication between horde and IMP ?

[Adrian Mak]

My server is running
postfix + Mailscanner + clamav + courier imap - mysql (virtual mailbox)

The role of the horde is to configure each component like IMP, Kronolith,
etc, so it provided user authentication with different mechanism e.g. mysql,
to setup user roles. Am I right ?

Then I am confusing about the IMP, webmail  component , which is talk to a
IMAP server in which has has it's own email users account for
authentication. For each users may have two userid/password ?? one is the
horde and one is the email account.

Also the horde - authentication, "What backend should we use for
authenticating users to Horde?" which allowed to select other horde
application to handle horde authentication. Does it mean that if I select
imp , then I can use my email address and password e.g. john at mydomain.com to
login the horde ??