Keep in active users email in Office 365

We have recently implemented Office 365 and migrated our mailboxes.
Since we have limited licenses I have to revoke licenses from the users who has left the organisation and assign them to the new ones.
We have a policy that we have to retain the emails of employees who have left for certain amount of years.
My question is, if I remove a user's account license, will it also remove his/her emails?
How can I keep user mailbox without license? Is transferring to the Shared Mailbox only option?
Allan AAsked:
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timgreen7077Exchange EngineerCommented:
yes you can convert the mailbox to a shared mailbox but there is a 50 GB limit on shared mailboxes at which point you will have to assign a license. under 50 there is no license needed.
Senior IT System EngineerSenior Systems EngineerCommented:
What about enabling it as the Archive mailbox ?
from memory, Archive mailbox is not counted towards the quota.
timgreen7077Exchange EngineerCommented:
An archive needs a mailbox with a license. the archive is the archive of a licensed mailbox. no archive mailbox by itself.
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Asif BacchusI.T. ConsultantCommented:
Timgreen7077 is correct.  Converting to a shared mailbox is the best option here and is the MS recommended option also.    Remember that shared mailboxes can be restricted to only certain people, or just one person, having access.  They do not have to be 'shared' with everyone.  

It seems as though you do not want to convert to a shared mailbox, however, unless I'm reading the intonation of your question incorrectly?  I might suggest that you look into an archiving solution with optional offsite encrypted storage if you are holding these messages for reference/legal reasons.  Something like MailStore or GFI MailArchiver, perhaps?  That way you don't need to worry about Office365 at all and you have access to those emails via a totally different platform.  (I am NOT affiliated with either company, I've just used them in the past and offer them as examples.)
Vasil Michev (MVP)Commented:
If you have legal/compliance requirements to retain users' data, converting to shared mailbox is not a good solution, as data can be removed/modified. Instead, you will have to place the mailbox on hold, which requires at least Exchange Online Plan 2 license. After doing that, if you dont need "active" access to the mailbox data, you can convert it to "inactive" mailbox, which is free and doesnt consume a license (but it still keeps all the data, immutably):

If you dont need to preserve data immutably, then you might as well consider using shared mailboxes. Note that you should not delete the corresponding on-premises object though, as this will cause the shared mailbox to be deleted in O365. Some other things to consider are mentioned here:

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Allan AAuthor Commented:
Thank you Vasil, We have Plan 2 licenses.
I will follow your recommendation and post the result here.
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