Export O365 to OnPrem

Hello everyone,

I know trend is on-Premises to O365 but I want to know,

How can I import O365 emails to an on-Premises mailbox. we cannot have domain trust between them. We acquired a company which have O365 for emails. We are an on-Premises shop for Exchange 2013 CU20.

What are my options?

Any lesson learns and experience will be help full.

thanks,

Zak

ZakBhai