Urgent CRM on Premise/Exchange

Hello,

Could you please help with the question below:

 The client is currently running CRM on-premise and their CRM has the ability to send and receive emails.

If they decide to go with O365 and have their Exchange server hosted by Microsoft, will this affect the capabilities of their on-premise CRM? Will they be able to preserve the functionality of their on-premise CRM?

Thanks,

Maarouf