Are old mail boxes lost when installing new office 365

When you migrate to Office 365, your old mailboxes are not lost, but they are converted to a new format. Here's what happens:

1. Migration process: When you migrate to Office 365, your old Exchange Server mailboxes are moved to the cloud-based Office 365 environment. This process is called a "migration" or "cutover."
2. Conversion to Office 365 format: During the migration, your old mailboxes are converted to the Office 365 format, which is based on the Exchange Online architecture. This conversion process is usually done automatically by Microsoft's migration tools.
3. New mailbox ID: Each mailbox is assigned a new, unique ID in the Office 365 environment. This new ID is used to identify the mailbox in the cloud.
4. Data preservation: The migration process preserves most of the data from your old mailboxes, including emails, contacts, calendars, and other items. However, some data may be lost or corrupted during the conversion process, especially if your old Exchange Server was outdated or had issues.
5. Retention policies: Office 365 has built-in retention policies that help preserve data for a certain period. These policies can be configured to retain emails, contacts, and other items for a specified amount of time.

To ensure a smooth migration and minimize data loss, it's essential to:

• Plan and test the migration process thoroughly
• Use Microsoft's recommended migration tools and best practices
• Verify the integrity of your data before and after the migration
• Configure retention policies to ensure data is preserved for the required period

In summary, your old mailboxes are not lost when installing Office 365, but they are converted to a new format and assigned a new ID. The migration process preserves most of the data, but some data may be lost or corrupted during the conversion process.