Issue

Gmail uses a label-based system that supports multiple nested sublabels, while Microsoft 365 relies on a traditional folder hierarchy with different technical constraints.

The migration path is not a 1:1 and a choice has to be made on if/how to replicate this email categorization.

Recommendation

Adopt the Option 2 “No Labels” approach for the migration which will not create duplicates.

Users should be informed that their Gmail labels will not be preserved. 

Background & Context

• Do not consider existing Gmail labels, and migrate all emails in the Outlook Mailbox.
• Consider Gmail labels and duplicate emails to store them in folders and subfolders of Outlook. Ex: if 3 different labels are applied on a Gmail email, 3 copies of this email will be done and each copy will be stored in a different Outlook folder corresponding to each original label.
• In Gmail, labels are tags applied to emails rather than physical boxes.
• Exchange Online use traditional folders, Gmail stores all your mail in one big bucket ("All Mail") and uses labels to filter what you see. 

Key Differences

Assumptions

• Users will receive guidance and training on the new Outlook folder-based structure.
• Migration tools will successfully move all messages without data loss.

Constraints

• Outlook’s folder model cannot fully replicate Gmail labels and hierarchy.
• Migration must fit within defined timelines, limiting extensive pre-migration adjustments.
• Not technically possible in Microsoft FastTrack to limit the number of labels, or to consider only the first label in the email duplication (asked to the MS product team)
• Not technically possible to list all existing labels by mailbox to further assess impacts

Impacts

Users will see changes in how their mail is organized after moving from labels to folders. This can cause confusion, slowdown in daily work and increase in support requests. 
Mailbox sizes may also increase, creating additional management overhead if storage limits are reached. Clear communication and guidance will be needed to ease the transition.

Options considered

Option 1 “All labels to folder"

For each label applied to an email in Gmail, one copy of the same email is created and stored in a corresponding folder in Outlook. The labels are all converted to Folders/subfolders and the mail is saved in all folder representing all labels. This means every mail will be duplicated by the number of labels attached.

Option 2 “No labels”

Emails are migrated without creating any folder in Outlook, and will all be in the inbox. Labels aren’t migrated at all. All mail lands in a simplified folder structure Inbox. Users lose their Gmail organization, but avoid duplication and hierarchy issues.

Option 3: Migrate labels to Categories (The technical team has determined that this option is not viable).

Some 3rd party tools try to transform labels to categories, but the functionality of categories is different from google labels. Categories are mainly a color coding system on items and do not provide a hierarchy as with google labels.

Evaluation

	Option 1 “All labels to folder"	Option 2 “No labels”	Option 3: "Migrate labels to Categories"
Technical Feasibility	124 mailboxes would reach the maximum storage capacity requiring cleaning and specific actions from their owners More difficult to revert due to duplicates & hierarchy	Easy to implement and easy to revert. 54 mailboxes would reach the maximum storage capacity requiring cleaning and specific actions from their owners	The mobile app has limitations compared to desktop and web versions in terms of Categories. Users can assign but cannot create, rename or delete categories in the mobile app.
User Impact	The “organization” of the mailbox is preserved: employees will find folders Outlook Folder hierarchy may conflict with the way Gmail labels are structured, resulting in a different folder structure than the initial label structure Degraded search experience (multiple results) Risk to create an “email multiverse” if “variations” of the same email loops are created by following-up on different copies of the same loop	Clean search experience (single emails, all in the inbox) Rules can be applied by the users after migration to restructure their mailboxes, in a way that is native to Outlook All mails will be in inbox and need to be restructured again in the new folder structure Users will be educated to use rules to automate as much as possible.	To search or filter on categories you need to create a search folder which is not portable so needs to be created on all devices and is not available on mobile app.
Operational Complexity	Estimated overall growth of mailbox sized: +30-35% resulting in more recurrent cleaning activities required and more upcoming mailbox size issues to manage	Leaner approach as data will not be duplicated	Categories are mostly color coding and not transformed to a folder structure and colors are limited to 25 colors. No tool can convert nested label hierarchy
GBU/BSA/GBS Feedback	7/11 votes	4/11 votes (November 25th "GBU connection" call)
Cost	Storage costs could arise on the long term (on top of the operational complexity)	Lower Cost and lower environmental impact	Cost of the tool needs to be considered, Implementation time and governance needs to be considered

Champions and IT Pioneers were consulted and both groups voted in majority for Scenario 2,
which is also the project’s recommendation (leaner and less confusing).

See also

The following section describes relevant documentation: