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.

Therefore, the migration path is not a 1:1 and a choice has to be made on if/how to replicated this email categorization.

Recommendation

Adopt the Option 1 “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

In microsoft Exchange, labels don't exist, the mails are organized in folders.
Therefore, when Migrating from Gmail to Exchange, two options are possible:

1. Do not consider existing Gmail labels, and migrate all emails in the Outlook Mailbox.
2. 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.

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 “No labels”
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 2 “All labels to folders”
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.

Evaluation

	Option 1: No Labels	Option 2: All Labels to folder
Technical Feasibility	Easy to implement and easy to revert. 54 mailboxes would reach the maximum storage capacity requiring cleaning and specific actions from their owners	124 mailboxes would reach the maximum storage capacity requiring cleaning and specific actions from their owners More difficult to revert due to duplicates & hierarchy
User Impact	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.	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
Operational Complexity	Leaner approach as data will not be duplicated	Estimated overall growth of mailbox sized: +30-35% resulting in more recurrent cleaning activities required and more upcoming mailbox size issues to manage
GBU/BSA/GBS Feedback	4/11 votes (November 25th "GBU connection" call)	7/11 votes
Cost	Lower Cost and lower environmental impact	Storage costs could arise on the long term (on top of the operational complexity)

See also

LM01-KDD002 - Gmail Migration to Exchange Online

[WIP] LM01_KDD00x - Migration to SharePoint

[WIP] LM01_KDD00x - Personal Drives Migration to OneDrive