Why convert instead of deleting or keeping the licence
If you delete a leaving employee straight away, you also throw away the mailbox. After 30 days that content is gone for good, unless you exported it or put a hold on it earlier. If you leave the licence in place "just in case", you pay every month for an account nobody should still use. Converting to a shared mailbox keeps email, calendar and contacts intact, lets several colleagues read it and drops the licence requirement as long as the mailbox stays under 50 GB.
What to know before you convert
- Licence first, then convert. Without a licence on the user mailbox you will not see Convert to shared mailbox. If you already removed the licence, put it back temporarily.
- Do not delete the account. The user account is still required as the anchor for the shared mailbox. Deleting it breaks the setup.
- Reset the password. Microsoft does not require a password reset, but without one the old credentials still work on the shared mailbox. Always reset, and keep sign-in blocked.
- Inbox rules are preserved. Forwarding rules and other mailbox rules come along. Check them immediately so no silent forward still points at a private address or a suspicious destination.
- 50 GB limit without a licence. Above that you still need an Exchange Online licence, or you clear large attachments first.
Step-by-step when someone leaves
- Block sign-in for the leaving employee and revoke active sessions so they can no longer reach Microsoft 365.
- Convert via Users > Active users > Mail tab > Convert to shared mailbox.
- Grant the successor permissions: usually Read and manage (Full Access) plus Send as or Send on behalf, so they can also reply.
- Set an automatic reply that names the new contact, internally and externally.
- Check mailbox rules and remove forwarding rules that no longer belong.
- Reset the password on the anchor account and leave sign-in blocked.
- Remove the licence if the mailbox is under 50 GB and there is no retention or litigation hold that still needs a licence.
If you only need new mail forwarded without opening the old inbox, forwarding to the successor can be enough. For handing over live customer work, converting is usually clearer.
Common mistakes
The biggest mistake is removing the licence before converting: the Convert button disappears and you have to put the licence back. The second is deleting the account "to tidy up": the shared mailbox then loses its anchor. The third is forgetting permissions for the successor, or leaving access open for colleagues who no longer need the mailbox. Record who has access and why, and remove permissions once the handover is done.
Already deleted the account? Restore it first, assign a licence again and wait up to 24 hours for the mailbox to come back before you can convert. That costs time and risk: better to do it right in one go.
How Floor ICT handles it
Floor ICT includes mailbox conversion in the standard leaver process. We block access first, convert the mailbox, grant the successor the right permissions, check mailbox rules and the automatic reply, reset the password and only then remove the licence if the size limit allows. That way customer email stays reachable without you paying for an account nobody should still use.