Large-Scale Email Archive Migration: e‑Purifier to Microsoft 365 to Acronis Guide

Knowledge Base: Large-Scale Email Archive Migration (e‑Purifier → Microsoft 365 → Acronis)

Overview

This guide describes the recommended enterprise method to migrate approximately 900 archived mailboxes from e‑Purifier into Acronis Email Archiving using Microsoft 365 as the ingestion layer.

Because Acronis archives by pulling data from live Microsoft 365 mailboxes, the migration path must be:

1. Export archive data from e‑Purifier

2. Import data into Microsoft 365 mailboxes

3. Allow Acronis Cyber Protect Cloud to automatically ingest and archive the historical mail

This approach is scalable, automated, and avoids manual Outlook imports which are impractical at this scale.

Architecture Flow

e‑Purifier Archive
        │
        │ Bulk PST Export
        ▼
Staging Storage (Local / Azure Blob)
        │
        │ AzCopy Upload
        ▼
Microsoft Purview Import Service
        │
        │ Mailbox Ingestion
        ▼
Microsoft 365 Mailboxes
        │
        │ Acronis Archiving Policy
        ▼
Acronis Immutable Archive Storage

Phase 1 – High‑Volume Export from e‑Purifier

For 900 mailboxes, manual portal exports are not feasible.

Request Bulk Archive Extraction

Contact e‑Purifier / Securicom support and request a bulk archive extraction.

Required Export Specifications

Request the export in the following format:

Format

PST files

Naming convention

user@company.com.pst

This naming format simplifies automated mailbox mapping during the Microsoft import stage.

Export Requirements

Storage Delivery Options

Because archive volumes can easily exceed several terabytes, request delivery via one of the following:

Preferred Option

Azure Blob Storage container

Alternative Option

Encrypted physical drive shipped to the migration team.

Storage Example

Azure Blob Container

migration-archives/

user1@company.com.pst
user2@company.com.pst
user3@company.com.pst
...

Phase 2 – Bulk Ingestion via Microsoft Purview

Do not import PST files using Outlook.

For large migrations Microsoft provides the Microsoft Purview PST Import Service, which performs ingestion directly into Exchange Online mailboxes.

This service supports parallel ingestion across multiple mailboxes.

Step 1 – Prepare the Import Environment

Required Permissions

The migration administrator must have:

Mailbox Import Export Role

This role can be assigned via:

Exchange Admin Center → Role Groups

Install AzCopy

AzCopy is Microsoft's high‑performance data transfer tool.

Download:

https://learn.microsoft.com/en-us/azure/storage/common/storage-use-azcopy-v10

Example installation location:

C:\AzCopy\azcopy.exe

Step 2 – Create an Import Job

Navigate to:

Microsoft Purview Portal

Data lifecycle management
    → Microsoft 365
        → Import

Create a new job.

Example name:

ArchiveMigration-Batch1

Select:

Upload your data

Microsoft will generate a SAS URL.

This is the secure destination endpoint used by AzCopy.

Example:

https://storageaccount.blob.core.windows.net/ingestion?sv=...

Step 3 – Upload PST Files Using AzCopy

Place all PST files into a single folder.

Example:

C:\MigrationPSTs

Run the upload command:

azcopy copy "C:\MigrationPSTs\*" "<SAS_URL>" --recursive

Example

azcopy copy "C:\MigrationPSTs\*" "https://ingestion.blob.core.windows.net/..." --recursive

Upload Best Practices

Step 4 – Create CSV Mapping Files

Microsoft requires a CSV mapping file that tells the service which PST belongs to which mailbox.

CSV Header Format

Workload,FilePath,Name,Mailbox,IsArchive,TargetRootFolder

Example CSV

Workload,FilePath,Name,Mailbox,IsArchive,TargetRootFolder
Exchange,,user001.pst,user001@company.com,FALSE,/
Exchange,,user002.pst,user002@company.com,FALSE,/
Exchange,,user003.pst,user003@company.com,FALSE,/

Mapping Column Definitions

Import Job Limits

Microsoft imposes the following limits:

Therefore 900 mailboxes require two import jobs.

Example:

Batch 1:

500 mailboxes

Batch 2:

400 mailboxes

Import Processing Speed

Microsoft processes ingestion at approximately:

~24GB per day per mailbox

Because processing occurs in parallel, large migrations can complete significantly faster than sequential imports.

Phase 3 – Acronis Automated Archiving

Once PST data is imported into Microsoft 365 mailboxes, Acronis Cyber Protect Cloud automatically begins archiving the historical mail.

Configure Acronis Email Archiving

Log into:

Acronis Cyber Protect Cloud Console

Navigate to:

Devices
    → Microsoft 365

Select:

Organization or user group

Apply a protection plan containing:

Email Archiving

Important Acronis Configuration

Ensure the archiving policy includes:

Archive start date = Beginning of mailbox

This allows Acronis to archive the historical data that was imported.

If the policy is configured for "new mail only", historical data may not be captured.

Monitoring Archive Ingestion

Verify ingestion via:

Acronis Console

Archive
    → Mailboxes

Each mailbox should show:

Archive collection active

Estimated Migration Timeline

Example scenario:

Total estimated project timeline:

2 – 4 weeks

Critical Migration Rules

PST File Size

Do not exceed:

20GB per PST

Large PST files can cause:

• Import failures

• Azure throttling

• Job timeouts

Message Size Limit

Microsoft Import Service skips messages larger than:

150MB

Naming Standards

Avoid special characters.

Recommended format:

lastname_firstname_export.pst

Retention Policies

Temporarily pause Microsoft retention policies before importing PST data.

Otherwise historical messages could be deleted before Acronis archives them.

Recommended Migration Strategy

Always run a pilot migration first.

Suggested pilot:

5‑10 mailboxes

Test the full pipeline:

e‑Purifier
   → PST export
   → Microsoft Import
   → Acronis Archiving

Validate:

• Folder structure

• Email integrity

• Archive ingestion

After validation, begin the full migration.

Troubleshooting

Import Tab Missing

Assign role:

Mailbox Import Export

CSV Validation Errors

Check:

• PST filename matches CSV

• FilePath column

• Mailbox UPN spelling

Slow Import Jobs

Possible causes:

• PST larger than 20GB

• Azure throttling

• Upload interruptions

Operational Checklist

Before migration begins ensure:

☐ PST files exported from e‑Purifier

☐ PST naming matches mailbox addresses

☐ Azure upload completed

☐ CSV mapping validated

☐ Import jobs created

☐ Acronis archiving enabled

☐ Retention policies paused

☐ Pilot migration tested

Appendix – Example Folder Layout

MigrationRoot

PSTs/

user1@company.com.pst
user2@company.com.pst
user3@company.com.pst

CSV/

batch1.csv
batch2.csv

Support References

Microsoft Purview PST Import Service

Microsoft 365 Data Lifecycle Management

Acronis Cyber Protect Cloud Email Archiving