Step 1: Evaluate Current Email Environment
To begin assessing your existing email environment, conduct an inventory of your existing infrastructure. Locate every mailbox currently used – including shared, distribution groups, service accounts and archived mailboxes – using either your current platform’s administrative console or reporting tools to produce an inventory listing all accounts by size and account name.

Step Two: Measure Total Data Volume
To evaluate total data volume, export a detailed storage report from your source system. Measure each mailbox including inbox folders, sent items, drafts and deleted items as well as personal archives (.PST or.OST files). Also take into account calendar data, contacts and tasks which also consume space across platforms – sum up these figures to get your baseline total data volume figure.

Step 3: Locating Large and Problematic Mailboxes
To identify large or problematic mailboxes, divide mailboxes by size to identify outliers. Mailboxes that exceed platform-imposed limits in their destination system require special handling; such as archiving, cleaning up or splitting. Establish a threshold (e.g. 50GB), with separate actions planned for any mailbox that exceeds it.

Step 4: Estimate Attachment and Inline Media Volume
Attachments often account for the largest chunk of mailbox storage. Run attachment analysis reports to understand how much data is stored as file attachments versus plain text, and factor this in when considering deduplication or external links as this will impact the final storage footprint.

Step 5: Plan for Growth and Buffer
Historical data does not accurately represent future needs. Take time to review email growth trends over the last 12 to 24 months and forecast storage needs over one to three years, then add at least 20-30% buffer volume when calculating volume for migration purposes to accommodate for growth without running into immediate capacity issues immediately after migration.

Step 6: Assess Destination Platform Quotas and Costs
Examine the storage limits and pricing tiers of your target platform to make sure that your estimated volume falls within its available plans, and whether any additional storage licenses or archiving solutions may be necessary to support it. Document any gaps between current usage and destination capacity.

Step 7: Document and Validate Your Findings
Document your findings by compiling them in a storage assessment report and sharing it with stakeholders for signature before starting to migrate data. This document can act as your go-to resource when it comes to capacity planning, licensing decisions and migration phasing throughout your project.

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