CloudM Continuity synchronises mail data from Microsoft 365 to Google Workspace in two phases: a one-time initial sync that migrates the last 30 days of mail, and ongoing delta syncs that keep the Google Workspace mailbox up to date with new changes. This article explains exactly what is included in each phase and how your M365 folder structure is mapped to Gmail.
Initial sync
The initial sync migrates the last 30 days of mail data from each user's M365 mailbox to Google Workspace. This is a bulk operation that runs once per user when they are first matched by a sync policy.
30-day sync window
The initial sync covers the most recent 30 days of mail at the time the sync begins. Older messages are not included. After the initial sync completes, delta syncs pick up all new and changed items going forward.
What is included
| Data | Details |
|---|---|
| Email messages | Full message content including subject, body (HTML and plain text), and all headers. Messages are imported in their original MIME (RFC 822) format to preserve fidelity. |
| Attachments | All file attachments are preserved within the MIME content and available in the Gmail message. |
| Sender and recipients | From, To, CC, BCC, and Reply-To addresses including display names. |
| Dates | Original sent and received timestamps are preserved. |
| Read/unread status | Unread messages in M365 are marked as unread in Gmail. |
| Importance and flags | High-importance messages and flagged messages are starred in Gmail. |
| Draft messages | Drafts in M365 are synced as drafts in Gmail. |
| Folders | The full folder hierarchy is recreated as Gmail labels, including nested subfolders. See Folder and label mapping below. |
| Categories | Outlook categories are recreated as Gmail labels grouped under an "M365 Categories" parent label. |
Delta sync
After the initial sync completes, delta syncs run on your configured schedule (weekly, daily, or hourly depending on your sync frequency tier). Delta syncs detect and apply changes made in M365 since the last sync.
Changes detected during delta sync
| Change type | What happens in Gmail |
|---|---|
| New message received | The full message (including attachments) is fetched from M365 and imported into Gmail with the correct folder label, read status, and flags. |
| Message deleted | The corresponding Gmail message is moved to Trash. |
| Message moved between folders | The old folder label is removed and the new folder label is applied in Gmail. |
| Read/unread status changed | The Gmail UNREAD label is added or removed to match. |
| Flag or importance changed | The Gmail starred status is updated to reflect the current flag state. |
| Category added or removed | The corresponding "M365 Categories" label is added or removed in Gmail. New categories are created as labels automatically. |
| Draft status changed | The Gmail draft status is updated accordingly. |
Delta sync does not re-sync message bodies
If a message body is edited in M365 after the initial sync (for example, a draft is updated), the delta sync detects the property change but does not re-import the message content. Only metadata changes (read status, flags, categories, folder moves) and entirely new messages are processed during delta sync.
Folder and label mapping
Microsoft 365 uses a folder hierarchy while Gmail uses a flat label system. CloudM Continuity maps between the two as follows:
System folders
| M365 folder | Gmail label |
|---|---|
| Inbox | INBOX |
| Sent Items | SENT |
| Drafts | DRAFT |
| Deleted Items | TRASH |
| Junk Email | SPAM |
| Archive | Archive (custom label) |
Custom folders
Custom folders are recreated as Gmail labels with the full folder path preserved. Nested folders use forward slashes in the label name to maintain the hierarchy.
| M365 folder structure | Gmail label |
|---|---|
| Projects | Projects |
| Projects → 2024 | Projects/2024 |
| Projects → 2024 → Client A | Projects/2024/Client A |
Categories
Outlook categories are mapped to Gmail labels under a dedicated parent label to keep them organised and separate from folder labels.
| M365 category | Gmail label |
|---|---|
| Red Category | M365 Categories/Red Category |
| Urgent | M365 Categories/Urgent |
Skipped folders
The following folder types are not synced because they do not contain standard mail content:
- Search folders — Virtual folders that represent saved searches, not actual message containers
- RSS feed folders — Contain syndicated content, not user email
Gmail label limits
Gmail allows a maximum of 10,000 user-created labels per account. Because each M365 folder and category becomes a Gmail label, organisations with complex folder structures need to be aware of this limit.
How CloudM Continuity manages the label budget
The system intelligently allocates the available label quota between folders and categories:
| Allocation | Limit | Notes |
|---|---|---|
| Total allocatable | 9,900 | Gmail's 10,000 limit minus a 100-label system reserve |
| Folder labels | Minimum 8,000 | Folder labels are prioritised because they represent the primary mailbox structure |
| Category labels | Up to 500 | Dynamically adjusted — if fewer categories are in use, more quota is available for folders |
| System reserve | 100 | Held back to prevent issues with Gmail's internal system labels |
What happens when the limit is reached
If a user's mailbox has more folders and categories than the available label quota, CloudM Continuity does not discard or flatten them. Instead, it uses a virtual items approach:
- Quota is checked before every label creation. The system queries Gmail to determine how many labels already exist.
- If quota is available, the folder or category is created as a normal Gmail label.
- If quota is exhausted, the folder or category is marked as virtual. It is tracked in the system's database but no Gmail label is created. Messages associated with virtual folders are still synced — they are imported into Gmail and tracked correctly, but without a dedicated label.
- When quota frees up (for example, if the user deletes folders in M365 and those labels are removed from Gmail), virtual items are automatically promoted to real Gmail labels. Folder hierarchy relationships are preserved throughout this process.
Label limits are per user, not per tenant
The 10,000 label limit is a Gmail per-account limit. Each user's mailbox has its own quota. A user with a simple folder structure will never approach the limit, while a user with thousands of folders may trigger virtual label handling. The system manages this automatically on a per-user basis.
What is not synced
The following M365 mail features are not included in the sync. These are either Outlook-specific features with no Gmail equivalent, or features that operate at the account level rather than the message level.
| Feature | Reason |
|---|---|
| Outlook rules | Inbox rules, auto-forwarding rules, and auto-responses are account-level settings, not message data |
| Out-of-office / auto-replies | Account-level settings that are not transferable between platforms |
| Sensitivity and classification labels | Microsoft Information Protection labels are M365-specific. Standard importance (High/Normal/Low) is mapped to Gmail stars. |
| Junk mail rules | Spam filtering settings are platform-specific and managed separately in each environment |
| Delegate access and permissions | Mailbox delegation and shared mailbox permissions are account-level settings |
| S/MIME signatures | S/MIME content is preserved in the message but not re-signed or re-encrypted for Google Workspace |
| Delivery and read receipts | Only the final read/unread state is synced, not the receipt tracking mechanism itself |
MVP scope: mail only
The current release of CloudM Continuity syncs mail data only. Support for additional data types (Drive, Calendar, Contacts) is planned for future releases. Sync policies allow you to select data types, and new types will become available as they are released.