Office 365: Understanding Mailboxes

Update 02/02/17 – While I appreciate the high amount of traffic that comes to this post, it is quite old, and many things may have changed. If you are interested in Dynamics 365, please check here.

There seems to be a lot of confusion around Microsoft Office 365 Mailboxes. In this post I will attempt to clear this up and hopefully save you some money in the process.

Microsoft Office 365 provides you with the ability to create different types of mail accounts for different purposes. Some of these account types require a paid license and others do not.

We often see clients who are paying for a license for a mail account that should be free.

The five types of mail accounts that you can create are:

  • Mailbox (Requires License)
  • Group (Free)
  • Resource (Free)
  • Contacts (Free)
  • Shared (Free)

I will first describe each type and when you should use it, and later get into some details.

Mailbox. These are for real people and these are the ones you pay for. Each living person in your organization that requires mail, will have a Mailbox. Each person can also have an alias for each domain that you have verified, i.e.,, You decide which of these is the default email address of the user, but mail sent to any of these addresses will all go into Mary’s inbox.

Group. Also known as Distribution Groups are free. These should be for internal use, i.e. When an email is sent to, 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, and the reply will go out to all members of the group also. Examples of typical groups might include, etc. 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 are free. Mail Contacts 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 (in the shared address book) who don’t need access to any internal resources.

Shared. Also known as Shared Mailboxes are free. This is the one 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. What happens is an email sent to this address goes into the inbox of the 5 recipients, just like an email sent to them directly does. If they reply, it comes from the individual replying. Even if the user creates a rule to automatically move these to a subfolder in their inbox, it does not take long before this proves cumbersome. What I find most Office 365 users doing next is biting the bullet and creating a paid account for sales so it can have a mailbox. 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. Don’t even try to tell me that you have not done this. While I am sure Microsoft loves you, this is what Shared Mailboxes are for. Plus they are a snap to administer with no end-user intervention required. As the most misunderstood account type, I am going to go through a step-by-step deep dive here on how to create them (you can click to enlarge any of the below images):

Step 1. Login to with administrator privileges. Click on either Admin then Exchange (up by your name), or Service Settings in the left sidebar and then the link at the bottom of the page. Either route will take you to the same place.

Step 2. In the Exchange Administration Panel, click on Shared and then the “+” to add a new Shared Mailbox.
Exchange Admin Panel

There are two parts to the creation of a Shared Mailbox, creating and editing properties. Most of the time you will not need the second step, and as shown below, the first step is as simple as:

  • 1. Give the shared mailbox a display name, this is the name that will appear in users’ outlook client for the new inbox
  • 2. Enter an email address, usually the same as the display name, and select the default domain from your verified domains.
  • 3. Click the “+” and add Full Access members (see explanation below)
  • 4. Click the “+” and add Send As members (see explanation below)


Let me clarify the “Full Access” and “Send As” roles:

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 shared mailbox when sending mail. For example, if Mary logs into the shared mailbox and sends an email, it will look like the Sales Department sent the email.

I mentioned a second part that may be optional, but then again you may require it. After you have saved your new Shared Mailbox you will be looking at a list of your Shared Mailboxes. If you double-click on one you will launch the Administration panel for that box. Here you can modify a lot of properties. The Mailbox Delegation link is where you would add or remove users, similar to the creation pane. If you need to add aliases, the Email Address link is where we would add them. You can click on the “+” and add for example, and or any other alias of a verified domain.


Okay, so how does this work on your user’s end? The new shared mailbox will automatically appear in their Outlook client or Outlook Web Access as show below:

Pretty cool huh?

Just hired a new salesman? Simply add them to the “Full Access” and “Send As” member list in the Admin panel for the Sales Shared Mailbox, and voila, they are now part of the team.

Feel free to add any information to this post I may have missed in the comments.


  1. Is it possible to create a free User for the purpose of Delegate access to all other paid mailboxes? An ERP email integration we are configuring requires Exchange Delegate access be assigned to one account for all the actual mailboxes in order for the Delegate to send/receive on behalf of.. everyone, but the Delegate will never really (need to) be a mailbox user itself. It is simply the account setup in the ERP configuration for Exchange synchronization. I have not found a way to assign a Delegate that isn’t already assigned/licensed to its own Exchange mailbox. This is on Office 365 and I would like to avoid paying for another Office 365 license to simply be this Admin User/Delegate. Thanks!

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  3. We have O365 E3 subscription. We usually create distribution groups in PowerShell so we could manage them in A/D. However the users cannot manage their distribution groups if we do it that way. So we’re starting to create them in EAC only so we can assign owners who can actually manage their group membership.

    I recently created 2 distribution groups in EAC. The user sends out monthly meetings using this group. When she reschedules meetings, some people are expanded and the rest are still collapsed in the group. She wants to know why and can they all stay collapsed. One thing she noticed is these people were in the Optional field instead of the Required field.

    I have searched and searched and now I’m hoping you might have the answer to this. Thanks!

  4. Billy

    For exchange 2013. AD user account with mailbox do you know what type of mailbox that need to associated with AD user accounts ? Shared, linked, room or user mailboxes ? The Ad account is for exchange administrator. Thank you

  5. Kevin G

    I would have liked to read the rest of the comments but white text on a dark background absolutely messes with my eyes. I can’t be the only one. Please add the option at the top of the page to flip the colors (i.e. dark text and white background).

  6. Alex

    Very informative. However you can send from a distribution group as that address so that the recipient sees the sender as the distribution group address now. Not sure if this is new since this article was written or not but you can in fact send from a distribution group as that distribution groups address.

  7. This was a great article and very helpful. Gave me what I needed to solve the problem I was working on.
    I did want to note that things may have changed since it was written. I don’t see the “full access” and “send as” settings in the new shared mailbox window. Rather I get only a “users” option and it states ” the following users have permission to view and send mail from this shared mailbox.”

  8. Eftihia

    I have max 10 users which I want to share the same inbox and filing. I consider a mail account to which all users will login from their pcs and their mobiles. Is there a limitation of the users that can use/login to the same mailbox. These users will also have their personal email set. All on exchange on line and outlook 2013.

  9. Is it possible to hide the delegate e-mail account on a PC so the operator only has access to a shared mailbox. Reason behind this question is I have a number of colleagues who do not need a personal e-mail account but do need a shared inbox.

        1. Brack

          Ah, ok…

          Thanks for writing the article, btw – I have several accounts that are set up as Groups that would function much better as Shared – very pertinent clarification!

  10. I want 5 people to use a shared mailbox which I would have to set up on 5 PC’s but I do not require them to have individual e-mail addresses do I still need 5 licences due to putting on 5 PC’s?

  11. Tom


    We have users on Exchange 2007, and also have SharePoint Online. None of our users have an 365 Outlook account.

    In these circumstances what is the best approach for creating a site mailbox?

    It seems to me that every user who needs to access the site mailbox will have to purchase an 365 Outlook account in addition to their Outlook 2007 ‘On-Premise’ account. Is this correct, or is there anyway around it?

  12. Stephanie J

    Great article! Clarified many nuances of share mail box permissions that were unclear for us. My end user community is continually prompted to input their password for shared mailbox (which we know doesn’t exist). Shared mailbox appears and is functional, but the credential nag won’t go away. I’d deleted ms.outlook entries from credentials vault and rebuilt but nothing seems to stop the endless credential request for a couple of my users. I can’t isolate the commonality in their environment. Any suggestions would help.

  13. Gene C

    We have a shared mailbox (smb) setup with 4 users…the problem is if 1 user deletes an email in his smb, it is removed from the other users smb…is it possible to keep the emails in the other users smb??

        1. Francisco

          You don’t need to set up external users to use distribution groups. You have to just remove the selection of sending mails to distribution group by authenticated users, then it allow any external user to send mail to the distribution group

  14. Tony Hoffensetz


    We have users utilising the Shared Mailbox with no issues when it comes to filing and managing the mail. The use of the shared calendar is almost perfect apart from the fact they do not get any notifications / reminders of shared appointments. Do you know if this is possible? There are 4 users all with full access and send-as permissions, Office 2013 and it automatically shows the shared mailbox.
    I know a room mailbox will do the alerts but this will not fulfill the needs.


  15. Aaron H

    Thanks for the clarification. I have one question re: shared mailboxes. I have several people who will have a domain user account but who do not have any need for an individual email address. I would want them to use the shared email address for all of their communications. Is that possible?

  16. MJ

    How do you add a “shared mailbox” to a distribution list/group. For example, we want “sales@” to be the shared mailbox, but want messages to leads_from_source_a@ delivered to the shared mailbox and an external address (contact) which is done through a group/disti list. Disti list can add external and named users(mailbox) but not shared mailboxes. Shared mailboxes seem to be the only thing excluded from distribution lists..

      1. Jackie N

        So I have been told but I have 4 users who have three shared mailboxes, one of which defaults to the shared mailbox address and the other two do not. They all appear to be set up the same with the same permissions – the users are in a group which is used on each of the shared mailboxes.

      2. Jackie N

        So I have been told but I have 4 users who have three shared mailboxes, one of which defaults to the shared mailbox address and the other two do not. They all appear to be set up the same with the same permissions – the users are in a group which is used on each of the shared mailboxes.

      3. Francisco

        the default behavior of not getting the sent from the shared into the sent items of the shared mailbox is wrong defeats the purpose of having a shared to some extent as the individual members who are sharing the mailbox and sending mails does not see each other mails causing confusion and reply again for the same thing already replied by some other team member who has shared the mailbox, this behavior has change and not acceptable, and to be treated as bad attitude by MS

    1. Georgie

      For the sent items to be saved in the shared mailbox settings you need to do the following;
      1. Close Outlook
      2. Open regedit.exe
      3. Browse to HKEY_CURRENT_USERSoftwareMicrosoftOffice15.0OutlookPreferences
      4. See if there is and entry for DelegateSentItemsStyle if so go to step 7 if not continue
      5. Right click then select New>DWORD32
      6. Type DelegateSentItemsStyle, then press enter
      7. Change the Value data for DelegateSentItemsStyle to 1
      8. Exit the registry
      9. Open Outlook and test

      This is the same when deleting a message from a shared mailbox, so to get the delete item to go into the shared mailbox’s deleted item you need to do the following;

      1. Close Outlook
      2. Open regedit.exe
      3. Browse to HKEY_CURRENT_USERSoftwareMicrosoftOffice15.0OutlookOptionsGeneral
      4. See if there is and entry for DelegateWastebasketStyle if so go to step 7 if not continue
      5. Right click then select New>DWORD32
      6. Type DelegateWastebasketStyle, then press enter
      7. Change the Value data for DelegateWastebasketStyle to 4
      8. Exit the registry
      9. Open Outlook and test

  17. Andy

    What about using site mailboxes?? I had the idea to setup a site where I would setup multiple site mailboxes for whatever I’d need them for. sales@ info@, possibly even contract employees (bill@) where I would invite them to the site/mailbox. I haven’t fully tested if external users could send from the site mailbox, but I think it’s worth asking about or looking into. Thoughts?

  18. konpro

    “The Full Access permission lets a user log into the shared mailbox”
    How can I log in without a password? (I guess without a license there is no pw and no access to the shared mailbox without outlook or owa for desktop)

    why is there a sent folder in the shared mailbox (license free), when it’s impossible to have an email in there. even when I send as/from shared mailbox it’s in my sent folder.

  19. Scott


    I am trying to set up a room resource and simply can’t find the links to do so. You mention a link top left called Exchange. I don’t have this. Any idea why?

    Thanks in advance


  20. Great article, Steve…
    However, i still have a clarification needed…
    I, admittedly, started using some accounts as groups, while others I used as Shared Mailboxes. My logic for doing one or the other at first was that some accounts (customerservice@, marketing@, etc.) needed all users to be able to truly read all emails and send from those accounts if necessary.
    For a couple accounts, I needed multiple people to be able to see the emails, but I didnt want them being able to inadvertently delete emails in that mailbox when they were the only copy. I have realized that atleast one of those groups needs to be a shared mailbox so I can actually send from that account.
    I am nervous that a user might mess up the shared mailbox / delete emails, etc. when they shouldn’t… so is there any permissions that can be applied to a shared mailbox that will allow them read access and send access from that account, but will not allow them to delete things?
    Thanks again!

  21. Thomas Ebling

    Great explanation and clarification.

    I still do not fully understand “where” the emails sent to e.g. is stored? (or to put it more bluntly, why it does not require a separate license, after all the emails for the shared mail need actual storage space etc.?)

    /Thomas 🙂

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