4 ways to save money preserving Leavers’ mailboxes

4 ways to save money preserving Leavers’ mailboxes

With nearly every migration workshop I attend now the same question comes up: “What do I do about my leavers”?

It’s inevitable people will leave your company.  Depending on your industry, you might have a high ratio of ‘live’ to ‘dead’ mailboxes.  For example, we have seen upwards of a 1:4 ratio in the financial sector.

The hard decision for a lot of companies comes when a migration is planned is whether those 'dead' archives/mailboxes should be moved.

For some it's a 'no brainer':  If there's a compliance need then all data needs to be retained but for others it's a 'nice to have'.

The problem comes then with cost: paying for a mailbox/archive licence in the new environment for staff that left a long time ago can be hard to swallow as most migrations are there to save money and improve working practices.  

So what can you do? If you’re lucky enough your target archive won't charge you for inactive mailboxes.   For example, with the introduction of ‘Wave 15’, Office 365 made it possible for you to preserve the contents of leavers’ (inactive) mailboxes indefinitely using something called ‘In-Place Hold’. 

According to Microsoft, once the mailbox has been put on In-Place Hold, the live mailbox can be deleted and the license associated it will be freed up. See the following reference for more information:


This means that you can in theory migrate ‘leavers’ mailboxes into the cloud, and then immediately put them on In-Place Hold, thus releasing the associated mailbox license.

However where there are licence costs associated with each users’ archive  you may want to look at alternatives.  Here are just a few ideas:

1. Export 'dead' mailboxes into PST files and back them up.  A downside of this approach is that PST files bring the risk of corruption and they're not easy to search should you need to, although this is a neat tool to help with this process.

2. Consolidate leaver’s mailboxes into one or more 'group mailboxes' in your target system, and give 'departmental heads' access rights.  This adds complexity to the migration process and could result in very large mailboxes.  You also have to think about how easy it will be to grant access to the various folders.

As an addendum to this point, if you're migrating to Office 365 watch out for the fact that Microsoft now expressly forbids the use of In Place Archives for storing mail belonging to multiple users. 


3. Keep your old archive with leaver's data only.  This is a slightly unusual approach as it means keeping on your legacy archive, but it will be more secure and accessible than using PSTs.

4. Export data to folders in a file share in .eml format.  You can use Windows access rights to give only the relevant staff access and deploy standard search tools to find information as and when required.

There are many different approaches and I have seen them all used - in some cases all by the same company.   There are also other considerations to throw into the mix, such as excluding migration of personal folders.

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