Comparisons
Microsoft 365 retention policies vs. a dedicated email archive
If you've read up on what Microsoft 365 preserves by default, you know the built-in answer to email retention is Microsoft Purview retention policies. And they're genuinely capable. So the fair question is: if Purview can preserve mail, why would anyone pay for a dedicated email archive? Sometimes the answer is "you wouldn't" — here's how to tell which side you're on.
What retention policies do well
A Purview retention policy tells Exchange Online: keep (a copy of) everything in these mailboxes for N years, even if users delete or edit it. Deleted items move into a hidden Recoverable Items area and stay retrievable via eDiscovery until the period expires. Configured org-wide with the right licensing, this covers the core preservation requirement — and it's included in licenses you may already pay for.
If you have E3/E5 across the board, an admin who knows Purview, and retrieval-via-eDiscovery is acceptable to your business, retention policies are a legitimate answer.
Where the two approaches differ
| Purview retention policies | Dedicated archive | |
|---|---|---|
| Setup | Someone designs policies, scopes, and exceptions — and keeps them correct as the org changes | Connect once; every mailbox (incl. new hires) is captured automatically |
| Licensing | Meaningful setups need Exchange Plan 2 / E3 / E5 on every covered mailbox | Works with any Microsoft 365 plan, incl. Business Basic |
| Who finds old mail | Admins, via eDiscovery / content search | Each user searches their own mail self-service; admins grant extra access explicitly |
| Tamper-proofing | Admins can change or remove policies later (unless irreversibly locked) | Stored outside the tenant; nobody — user or admin — can alter or selectively delete archived mail |
| Employee leaves | Works if the hold existed before deletion → inactive mailbox; retrieval stays admin-only | Archive simply remains, searchable, after the account is gone |
| Independence | Preserved data lives inside the tenant it's meant to protect | Separate copy on separate infrastructure, exportable as standard .eml |
The three differences that decide it in practice
1. Who does the finding
With retention policies, preserved mail is retrievable — by an admin, through eDiscovery. Every "can you find that email from 2023?" becomes an IT ticket. A dedicated archive turns that around: people search their own archived mail like they'd search Outlook, and nobody queues for an admin. For a 20-person company without a full-time IT department, this difference alone usually settles the question.
2. Who guards the guards
Retention policies live inside the tenant, controlled by the same admins whose actions an archive is supposed to make provable. If a policy is quietly shortened, preserved mail ages out. An external archive holds its copy outside the tenant, where changing history isn't a settings change — for questions like "prove this mail existed and was never altered", that separation is the point.
3. What it costs, honestly
"Included in E3" is only free if you're on E3 anyway. Upgrading Business Standard mailboxes to E3-class licensing purely for retention typically costs more per user than a dedicated archive — before counting the admin time for Purview policy design and every eDiscovery request afterwards. Comparing real numbers for your own mailbox count takes ten minutes and usually surprises people.
If you land on "dedicated archive"
mailvault365 is exactly that, built only for Microsoft 365: connect your tenant with read-only permissions, and every mailbox is archived continuously — tamper-proof storage, full-text search, archives that outlive departed employees, $4 per mailbox per month with any license tier. And because it never writes to your tenant, it coexists happily with any retention policies you already run.
Still weighing the fundamentals? The backup-vs-archive distinction trips up even experienced admins: Email archiving vs. backup: two tools, two completely different jobs.