I am having some pretty much f***ed up setup - I'm currently have some sort of dedicated server where I host several domains with cpanel. All the emails are being processed by Open-Xchange server (hosted on other machine) as cpanel does have some kind of OX addon that jumps in between and coordinate everything.
I have root access to cpanel server but not to OX one.

Right now I want to migrate to another cpanel server (this should be doable with an ease) and ZCS OS instead of OX.

I have several hundred of email accounts and does not know these accounts passwds.

Does anyone have any idea on how to migrate emails from OX to ZCS? I don't. Is there anything I can ask OX hosting company to do for me that would help mi migrate existing emails to ZCS (to perform some export!?)?
If it means anything, it seems to me like cpanel has copy of each single email any account received till today.

Currently I have no idea from where to start from. Any idea would be highly appreciated.

If there's any other info that can shed some more light on the current setup, do not hesitate to ask.