Same mailbox with different logins

[Evgeniy Arbatov]

Hello,

A question: I want users authenticating with two different usernames
to Cyrus IMAP to be able to access the same mailbox.

For example, I wish this to be the case ("login name" -> "mailbox"):

username -> user/firstname.lastname at domain
firstname.lastname at domain ->  user/firstname.lastname at domain

What would be the way to proceed?

At the moment I have:

username -> user/username
firstname.lastname at domain ->  user/firstname.lastname at domain

With the two mailboxes being completely separate.

Thank you in advance!

Best regards,
Evgeniy