Need help with mail server clustering

[Yu Meng Chong]

Hi all, 

Happy Chinese New Year! Hope everyone on this list is safe (and still safely in their jobs!)

I need some advice on something -- this is a theoretical question (for now), but it has been bothering me for a while because of a problem I have been seeing in my little part of the world. 

In this scenario, I need to design a mail infrastructure solution that involves several mail servers. Outgoing mail will go through one single server. Incoming mail and user mail boxes will be spread over several servers (because each user wants extremely large storage, say 100GB) and we will be using IMAP. There is just one requirement:   

On user mail clients, they only need to specify one IMAP server (say, imap.company.com). The user does not need to know the actual server where his/her mailbox resides. 

Are there any write-ups about this kind of scenario that I can read? I have not been successful Googling, but it may be that I am not defining my search properly. 

The reason I ask is because there is a service provider in Singapore that is using this kind of infrastructure, but there seems to be something wrong with the mail routing, but I'm not getting any straight answers yet on the cause or possible solution.

Regards,
pascal chong