Questions about different type of accounts

[bud.golf4]

hello,

What is the different type of users,

user account.
internal user account.
group account.
ressource account.

In fact i search a solution with kolab to do this:
One person receive all emails for a department
(department at company.com) and resend the emails to specific
internal account that can not receive emails from the internet
(user at here.com) i want that they just can send emails with the
department at company.com in "sender"

how can i do this with kolab.

Thanks.

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