This article describes how delta migration works during mail migrations.
Overview
Cloudiway migration internally stores a reference (messageID or ItemID) to all items it migrates. When you remigrate a mailbox (delta pass), items that have already been pushed are not migrated again.
The delta pass mechanism ensures that no duplicate content is created in the target in order to avoid duplications.
90-Day Window
After the first migration pass is complete, you have up to 90 days to perform delta passes and final cutover for that mailbox.
How Delta Migration Works
Important: Cache Behavior
Therefore, if you need to remigrate an entire mailbox, you would need to:
- Use a new Cloudiway license
- Delete the user from the Cloudiway user list
- Recreate the user entry
This will be considered a new user and will consume a new Cloudiway license.
Domain Moved?
Mails
Exchange / Microsoft 365 as Source
Changes after migration are propagated. This includes:
- Mail deletions
- Moving mail from one folder to another
- Mail marked as read
- Other modifications
Google as Source
Deletions from Google are propagated.
Other Sources
Changes are not propagated. The respective APIs do not propose a way to detect changes between two passes.
Calendar
The calendar migration engine works as a synchronization engine. Depending on the scenario, updates and deletions of appointments can be propagated during delta passes.
| Source | Changes Propagated | Notes |
|---|---|---|
| Exchange / Office 365 | Yes | Updates and deletions are propagated |
| No | No APIs to detect changes between passes | |
| Other sources | No | Would require reading entire source and target |
See more about calendar migration in the Calendar Migration Guide.
Contacts
During a delta pass:
- New contacts are migrated
- Deletions and modifications are not propagated
Tasks
During a delta pass:
- New tasks are migrated
- Deletions and modifications are not propagated
Migration to an Existing Mailbox
Cloudiway adds items to an existing mailbox. It does not touch, modify, or delete items that have not been pushed by Cloudiway.
This means that:
- Existing items are not overwritten
- If you entirely migrate a mailbox 2 times (with 2 Cloudiway licenses), it duplicates the items: The second migration is considered as a new migration to an existing mailbox with items.