Convert a Exchange online mailbox to shared mailbox

There may be times when a user leaves your organisation and you need to free up their Office 365 license for the next user. This sometimes presents us with the need to maintain the email’s stored within the old users mailbox and continuing to receive new email that is sent to their SMTP address. The simplest way to achieve this is to convert the mailbox to a shared mailbox as long as the account is consuming under 10GB this isn’t a problem. Once we have pruned the account down to under 10GB if necessary we can then convert the mailbox to a shared mailbox.

1. Connect to Exchange online using powershell.

2. Convert the mailbox to a shared mailbox using the following command:

Set-Mailbox -type:Shared -ProhibitSendQuota 9.75Gb -ProhibitSendReceiveQuota 10Gb -IssueWarningQuota 9.5Gb

3. Check in you organisation’s Exchange online portal that the mailbox is listed under shared mailboxes.

4. Remove the relevant license from the user and you’ve now successfully preserved the email in the mailbox. All new email sent to the SMTP address will now be delivered to the shared mailbox.