Storing Ex Employee emails while making it accessible and searchable without PST Files

bb_on used Ask the Experts™
We use Office 365 for office email and Dropbox/Egnyte for shared file storage.
When a user leaves the company, I want to be able to easily access/search their email but I do not want to maintain their account indefinitely.
I also do not want to maintain multiple 2 to 10 GB PST files.

I am looking at using Migrationwiz to migrate old employee O365 accounts to a single O365 account under a shared email account (I.E.
This would also allow me to set their email addresses as an alias on the shared account.

Does anyone have a better solution?
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The most important question here is whether you *must* ensure immutability of the data for compliance requirements. If so, the best solution is to use Inactive mailboxes, which are free and keep the data in-place in O365, allowing it to easily be searched/exported if needed:

You can easily convert a user mailbox to shared, which is free up to 50GB. Shared mailboxes however do not preserve data immutably, you will need to put them on hold for that, which in turn requires an Exchange Online Plan 2 licenses.  Moreover, if you use a single shared mailbox to store messages from multiple user mailboxes, you will be violating the  terms, so I would advise against that route.

Some other considerations are listed here:
bb_onIT Manager


Thank you Vasil.
A reply that I got from which I marked as best answer states as follows:
DragonsRule wrote:

If you convert the account to Shared it doesn't use a license.

That is one way and preferred when you want to give access to the mailbox  to another user, like their supervisor or the one taking over. Be aware you can't delete the user, just remove the licenses.

Another is to implement a tenant wide retention policy and/or legal hold. This will allow you to use the e-discovery tools to search eveything, even deleted files and e-mails. This requires at least Office 365 E3.

the data is still in Exchange Online but its only accesible by using the eDiscovery tools.

I have applied a policy that keeps all email and OneDrive content for my users for 7 years, regardless of anything else.

Once a you place mailbox in hold (in-place or litigation) you can delete the user account or remove the license. It becomes an  "inactive mailbox".

See Remove a former employee from Office 365.

You can assign eDiscovery roles to users.

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