Exchange 2016-Office 365-Hybrid

I need to configure hybrid  environment for one of our client (exchange2016 on premissoffice 365)
Client is allready using office 365 couple months without hybrid connector(without Active Directory hybrid syncronization)
Client has 150 AD users on premisse and another 150 office 365 users separately.
If I configure hybrid environment do I need to delete office 365 users and start all over.He has 150 licence.
Any suggestions are welcome
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Vasil Michev (MVP)Commented:
No. You can either leave them as they are, or if needed, "link" them to the AD accounts. In either case, deletion is not mandatory, nor recommended in any way, unless you are completely sure there is no data they want saved.
timgreen7077Exchange EngineerCommented:
@Vasil is correct, there is no need to delete the O365 users as long as you are planning to use both set of user's (cloud and on-prem) under the same tenant.
AndyAuthor Commented:
Thank you
Im not sure if client wants to use both set of users(cloud and on-prem) and whats the implications and how it looks like.
Im just investigating what are my options and what to offer.
How can I „link“ them?
He has 150 licence
Any advice would be greatly appreciated
timgreen7077Exchange EngineerCommented:
Here is a link to give you a few scenarios and solutions how to resolve issues you can run into depending on the option you choose since you have users using O36 accounts and users using on-prem accounts.
Vasil Michev (MVP)Commented:
In general you have two options:

1) use Soft-match as detailed here:

2) use hard-match:

Keep in mind that you should NOT link any users that have mailboxes on both locations.

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