Integrate mail system between O365 and mail system on-premise

[techno1795]

Dear all friends and experts 

From my customer requirements.

They have a system email on-premise ( I do not know what is their product of their mail system ( exchange or open resources ..).

So that., they want move some users from on-premise to O365, ( 50% on-premise, 50% on O365). As my understand ( I am new in O365), I need deploy a Hybrid exchange between On-premise vs O365. Is this right solution ?.

May you let me know that hybrid between O365, the on-premise must be run Exchange product ?, Exchange online does not support other products ?

Please help me, and clear for me some information. 

Thank you so much !

Lee

[#2]

You need to have Exchange on premise to have a Hybrid environment.

You may have a look at this.

https://docs.microsoft.com/en-us/exchange/exchange-hybrid

[#3]

First thing you need to do is to find out what On-Premises e-mail system you customer has...if customer has Exchange 2010 / 2013 / 2016 / 2019 then this scenario is fully supported under a hybrid deployment so you can do what you have been asked for. But if your customer does not have Exchange, the hybrid request cannot be done in the same way and you will need to evaluate what your options are here such use e-mail redirection for migrated users, partially domain validation in Office 365, etc