Stubbing Hell

How poor shortcut handling can derail your email archive migration to Microsoft Office 365

Posted by Darwin Lee on Jul 12, 2019 Last updated Jan 17, 2022

Imagine trying to open an email post-migration to Microsoft Office 365, and you just get …. nothing.

…or a whole bunch of emails, that you thought you’d deleted years ago, suddenly turn up unannounced in your inbox.

These are the kinds of things that can happen when you migrate email archives into Microsoft Office 365.

Although migrating archives to Microsoft Office 365 is a well-trodden path, the role that stubs (aka shortcuts) play in your migration success can be massively overlooked.

What are email stubs? / What are mailbox stubs?

An email stub is a computer file that provides a shortcut to a full email message stored in an archive / email server. When the email stub file is accessed, the user is able to view the full email and any attachments immediately.

What is email stubbing?

Email stubbing allows end-users to access their emails while reducing the storage requirements on your email server. The stubbing process means that emails take up dramatically less storage space, in turn improving server performance.

When archived these emails only show the header information, rather than the full email content and any attachments. End users don’t see any difference between a stubbed email and the original email. The original emails are relocated to the email archive and can be accessed via a link within the corresponding stub file. Over the years, millions of stubs are created. Although on the surface it looks good, it can result in a number of issues as we’ll explore.

Email Stubbing Issues when migrating to Microsoft Office 365

So, let’s look at the top 5 stub related problems to contemplate when you migrate to Microsoft 365:

1 – Forwarded stubs

Forwarded stubs that don’t migrate. Your archive migration failed to identify and migrate any items (shortcuts) that were forwarded from a co-worker.

2 – Sizing folders containing stubs

Public folders containing stubs are difficult to size. If you plan to migrate legacy public folders to the ‘modern’ public folder service in Office 365, you need to be able to ‘chop up’ your public folders into sub 100GB chunks.


Getting a fix on exactly what size your public folders are when they contain shortcuts is quite a challenge. This is especially true when a shortcut might be a few KBs and the archived item it links to could be 10MBs (or whatever you’ve set your message size limit to in Exchange). Often the best strategy here is to re-hydrate your public folder archives back into Exchange (on-prem) first, and then migrate. That way, you know exactly what you’re dealing with.
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3 – Stubs you don’t know exist

Stubs in public folders you think aren’t there! Although you might have blanket archiving rules in place for user mailboxes – but not public folders – think again. One organization we encountered recently was adamant that its public folders had not been archived (therefore they didn’t need to be considered as part of the migration project). Wrong! On inspecting the message class of the public folder contents (e.g. IPM.NOTE.EnterpriseVault.Shortcut), they found a high proportion of archived emails. In short, users had been busy dragging and dropping stubs to archived items into public folders – and why wouldn’t they?

4 – Zombie stubs

Zombie messages – i.e. deleted stubs that come back to life post-migration. Enterprise Vault, for example, does a good job of synchronizing the status and location of shortcuts. However there are some scenarios where deletions might not be picked up. This can happen where users drag their shortcuts into the Outlook deleted items folder, rather than highlighting them and using the right-click delete option that links with EV. It also occurs when users delete an entire folder (that contains a proportion of stubs). Having deleted items reappear to end-users is a great source of concern!

5 – Missing flags and categories

Ultimately, because stubs ‘look and feel’ like regular emails, end-users treat them just like any other email. This includes filing them into different folders (see also point 3), setting follow-up flags and categories, and so on. If the status of emails, including their current folder location or category, is lost post-migration, the most organised of your end users are effectively penalised and their productivity is impacted. There are lots of other stubbing hell scenarios that apply. They vary from archive to archive – even down to the version of the archive client, you’re running.

There are lots of other stubbing hell scenarios that apply, and they vary from archive to archive – even down to the version of the archive client you’re running.