Office365 is a fantastic mail platform with many options. However, due to the large amount of options, certain features are often unexplored. Specifically, there seems to be a lot of confusion regarding O365 mailboxes. I frequently see offices paying for mailbox licenses when a different free mailbox could’ve been used. In this article I will review each type of mailbox and their purpose.

Mailbox – These are for real people and are the ones you pay for. Each person in your organization that requires mail should have a Mailbox. Each person can also have aliases and mail sent to any of these addresses will all go into the inbox.

Group – Also known as Distribution Groups. These are free and should be for internal use, i.e. When an email is sent to a distribution group, each person who is a member of this group will receive an email into their own mailbox. If they reply, the reply will come from the user. If reply all is used, it will go out to all members of the group. Groups can also have aliases like Mailboxes.

Resource – Also known as Equipment Mailbox or Room Mailbox are free. These are used for reserving and coordinating Rooms and Equipment. For example or By including a Resource in a meeting request or calendar item, you are reserving the Resource for that time period. When you create your calendar event you can look at the Resource to check its availability.

Contacts – Also known as Mail Contacts. Mail Contacts are free and typically contain information about people or organizations that exist outside your Exchange organization. Mail contacts can appear in your organization’s shared address book and other address lists, and can be added as members to distribution groups. Each contact has an external email address, and all email messages that are sent to a contact are automatically forwarded to that address. Contacts are ideal for representing people external to your Exchange organization and don’t need access to any internal resources.

Shared – Also known as Shared Mailboxes. These are free and are generally the one mailbox type that is not being utilized properly, if at all, by most organizations. Let’s say you have a generic email address on your website for  that you want five people in your organization to receive. Too often we see these being setup initially as Distribution groups which cause issues when replying to emails. What I find most Office 365 users doing next is creating a licensed mailbox and then each of the five people need to add the account to their Outlook client with the username and the password for the sales account. Shared mailboxes allow all users to access the assigned mailbox from their account (via Outlook or OWA) and interact with is as a normal mailbox. The downside to shared mailboxes is that they cannot login on their own. You have to have delegate access from a real mailbox to access the shared mailbox. Another use for shared mailboxes is keeping a mailbox active for deprecated users. For example, say has left the company. You want to keep his mailbox active in case anything is delivered but don’t want it forwarded and cluttering other user’s mailboxes. You can convert John’s user mailbox into a shared mailbox. This will free up a license and keep the mailbox active. Anyone who is the assigned Full Access to the mailbox would be able to manage the shared mailbox.

Lastly, let’s review access types on all mailbox types:

Full Access: The Full Access permission lets a user log into the shared mailbox and act as the owner of that mailbox. While logged in, the user can create calendar items; read, view, delete, and change email messages; create tasks and calendar contacts. However, a user with Full Access permission can’t send email from the shared mailbox unless they also have Send As permission.

Send As: You will usually want this. The Send As permission lets a user impersonate the mailbox when sending mail.

Send on Behalf: The “From” address in any message sent by you will indicate that the message was sent by you on behalf of the user that granted you this permission.

With the above, you can utilize the right mailbox for the right job and start saving your company in licensing costs!