Office 365: Understanding Mailboxes

Update 12/21/17 – I originally wrote this post in 2013, and it was been the most viewed post ever. I have been focused on other things and this post information had been quite out-of-date. I asked my good friend Carl Mazzanti, owner of Micrsoft Gold Partner eMazzanti, and all-around expert in Office 365, if he would update this for me, and he graciously agreed.

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.

ConfusedMicrosoft 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.

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.

Because of the confusion, we often see clients who are paying license fees for mail accounts that can be free if set up and used properly.

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

  • Mailbox (Requires License)
  • Distribution Group (Free)
  • Resource (Free)
  • Contacts (Free)
  • Shared (Free)
  • Office 365 Groups (Free)

I will describe each type, how it should be used and how to save that cash. New since the original post, Office 365 Groups are designed to enhance collaborative work.

Mailbox (paid license)

This is where it all starts. When you purchase a license that includes Exchange Online, you will be getting a mailbox. This is what you add to your various mobile devices and log into every day with your email and password. Your Exchange Online mailbox is typically your primary email account.

Popular plans that include Exchange Online:

  • Exchange Online (Plan 1)
  • Exchange Online (Plan2)
  • Office 365 Business Essentials
  • Office 365 Business Premium
  • Office 365 Enterprise E1
  • Office 365 Enterprise E3
  • Office 365 Enterprise E5

Distribution (no cost, comes with subscription)

Distribution groups are emailing lists. When you create a distribution group, you add members and assign an email address to the group. If someone sends an email to the group email address, each member of the group will get a copy of the email. When responding to an email, the response can be from the individual member’s mailbox OR the distribution group email address.

Distribution groups can be used internally and externally. For example, you can use an internal distribution group for your departments or the entire staff (; OR, you can use an external distribution group for your website (;; There are no credentials for this type of mailbox and they can’t be added to mobile devices. But, that’s fine since the email will be routed to a group member’s email account.

Resource (no cost, comes with subscription)

Resource mailboxes are for physical locations or equipment, like conference rooms or a video-conferencing device. You add the room or equipment’s email address to an email’s list of recipients like it were an actual person. Then, open the scheduling assistant in Outlook to see what times are available.

Contacts (no cost, comes with subscription)

Mail Contacts are email addresses (usually external) with contact information that are added to your organization’s Global Address List—a simple way of keeping frequent contacts available to your organization.

Adding a person to Contacts will also allow you to add that person to one of your organization’s distribution groups. For example, if you have an internal distribution group and want an outside consultant to also receive emails to the group, you add that consultant as a contact first, and then add him or her to the distribution group.

Shared (no cost, comes with subscription)

A shared mailbox is quite literally that. It’s a free mailbox that is created and assigned to users in your organization. There’s no end user configuration, so once the user has been assigned to the shared mailbox, their Outlook will automatically add it below their primary inbox. It even comes with its own calendar.

When anyone emails the shared mailbox, the email will be delivered to the inbox of the mailbox and anyone assigned to it will be able to see it and act on it. Shared mailboxes are a great way to keep notifications from a service or your website from cluttering your primary inbox. Since it is defined as its own mailbox, you can export the entirety of its content as a PST file.

A few caveats:

  • Anyone assigned to the shared mailbox will have control over the mail. So, if one person deletes an email, moves an email to a subfolder or replies to an email from the inbox, it will be reflected across all assigned users.
  • Anyone assigned can reply to email and it’ll come from the shared mailbox email address. Sometimes, however, one person will reply but another won’t realize that and also send a reply.
  • There are no credentials to a shared mailbox, so you can’t add it to mobile devices. Don’t rely on a shared mailbox as a primary mailbox.
  • You do not get the typical “new email” popup like your primary email inbox. Here are a few workarounds.
  • Shared mailboxes only work for Outlook 2010 and above

Saving Money with Shared Mailboxes

The Shared mailbox is grossly underutilized, costing organizations fees for unnecessary licenses. For example: 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, these are set up initially as Distribution groups. An email sent to the group 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.

Office 365 Groups (no cost, comes with subscription)

This is the newest type of mailbox from Microsoft designed to enhance collaborative work. The setup is just like a Shared Mailbox. You create a name and email address, and assign users. When you create an Office 365 Group, you get a mailbox, shared calendar, a document library stored in the cloud, a OneNote Notebook, a SharePoint team site and a planner.

You can even invite external guests to Office 365 groups if you want to have them join in on the conversation and collaboration. They also allow you to create a conversation, so new members won’t miss out on previous emails. Conversations are stacked inside the workspace, and when you select one, you’ll see the original message PLUS all the replies in order, similar to a forum. You can even LIKE a message.

All the Office 365 Group features are found on Outlook 2016, the Outlook Web App, Outlook 2016 for Mac, Outlook for iOS/Android/Windows Phone, and the standalone app, Outlook Groups—available for iOS and Android.

Subscriptions that include Office 365 Groups:

  • Office 365 Business Essentials
  • Office 365 Business Premium
  • Office 365 Enterprise E1
  • Office 365 Enterprise E3
  • Office 365 Enterprise E5


Creating a shared mailbox

  1. Login to as an admin. Click on Shared Mailboxes.
  2. Choose a name for the mailbox. This is what recipients will see when they get receive an email from this mailbox.
  3. Once created, click on Add members to this mailbox
  4. Click on Add members to select who will be assigned to the mailbox
  5. Type in the user’s name, check their name, and save
  6. Once you’ve added your users, you can click on the shared mailbox and review the properties including:
      • Email aliases
      • Email forwarding
      • Automatic replies
      • Sent items
      • Email apps
    • Membership
      • By default the “Read and manage” and “Send as” permissions are set for any user. Read and Manage allows the user to create, read, view, delete, and change email messages, create tasks and calendar contacts. Send As allows the user to reply to email as the Shared Mailbox address.
    • Litigation hold (in Office 365 Enterprise E3 plans or higher)
    • Show in global address list


Creating an Office 365 Group

  1. Click on Groups, and + Add a group
  2. Make sure Office 365 Group is the selected type
    • Select a name
    • Group ID (email address)
    • Description (optional)
    • Privacy
      • Public – Anyone can see group content
      • Private – only members can see group content
    • Language
    • Owner


To access this new Office 365 group and all it’s resources, go to Outlook (desktop or online) and you’ll find it underneath you mailboxes. You’ll also see the resources including conversations, files, calendar, notebook, planner, and site. Now get to collaborating!


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

Special thanks to our good friends and Office365 experts at eMazzanti Technologies for helping me with this updated post. Give them a shout if you are looking to migrate to Office365.

Add your thoughts below, just don’t pimp your stuff on my blog 🙂


  1. James Miller

    Mail boxes is very important and useful. You share the info about mailboxes is really helpful for me. Nice information you share on this blog. Thanks!

  2. Farid fs Sotoudeh

    @Conpro , you can access SMB via OWA by clicking your account pic and add another mbx. You wont be asked for a password if you are a member or have permissions.

  3. Alibaba

    Hi Steve, just a rough thought – is there any package is available by Office365 – where unlimited mail box under a single package? Can you name it to me?

  4. James Bertram

    I’m actually having a similar dilemna for a new service we are rolling out. We were hoping for a barebones mailbox (even 50MB would suffice) with associated passwrd that it could ingest data from.

  5. Greg Archambault

    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!

  6. E Long Powell

    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!

  7. Mike

    clear and concise info. use this link to give people an easy way of understanding mailboxes without having to pull my hair out…thanks again.

    • Steve Mordue

      Thanks, but bear in mind that this post is quite old…

  8. 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

  9. 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).

  10. 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.

  11. Edwina

    Really good article… one other question. What about for applications that both send and receive emails. Do they need a license?

  12. T. Thomason

    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.”

  13. 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.

  14. Ashley

    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.

    • Brack

      Why not set up a mailbox (i.e., and give the account information to all 5 people? I don’t know that there’s a limit on the number of devices that can check an email account, so that might be the simplest solution.

      • Steve Mordue - CEO

        I think she was hoping to accomplish this with free shared mailboxes as opposed to a paid regular mailbox

        • 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!

  15. Ashley

    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?

    • Steve Mordue - CEO

      Yes. Shared Mailboxes have no credentials, they use the credentials of their delegates.

      • Ashley

        Thank you Steve. Kind Regards Ashley

  16. Vijau

    We are receiving emails in defined users mailbox but when someone reading the mail first it is showing read in all users outlook, any changes I have to do on Office365 portal?

    • Steve Mordue - CEO

      That is correct behavior, user can right-click and Mark unread

  17. 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?

  18. 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.

  19. itkom

    Is there any way to open Shared mailbox in Outlook 2007?

  20. Gene C

    the distribution group (dg) is working well including the send as…but is there any work around so the dg email is the default send as??

  21. 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??

    • Steve Mordue - CEO

      you probably want to use distribution groups for this

      • Gene C

        the wrinkle with that is that an external user must be set up first to send an email to the group…is there a work around??

        • Steve Mordue - CEO

          distribution group email does not require a license, a shared mailbox is a single box that is shared

        • 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

  22. 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.


  23. 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?

    • Steve Mordue - CEO

      Sorta, the way shared mailboxes are shared is via delegation to one or more other Exchange users, so they would each need an active mailbox, that does not mean they have to use it for anything though.

  24. monica

    Great article! I have a query. In a shared mailbox, if I want to count how many mails has, say Mary, sent from the shared mailbox, is that possible?

  25. JBR

    Great article

    – Do you know what is the real (technical) difference between Equipment Mailbox and Room Mailbox? – A link to a true definition would be nice.

    • Steve Mordue - CEO

      Not sure there is a difference

  26. 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..

  27. Jackie N

    is there anyway to force the “Sent from” address to the shared mailbox address instead of the users personal address when replying from a shared mailbox?

    • Steve Mordue - CEO

      This is the default behavior

      • 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.

      • 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.

      • 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

    • 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

      • Francisco

        thank you much, you are the best


      • Andrey

        Is there any way to do same thing with web app?

  28. 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?

    • Andy

      PS, nice article by the way. cleared some things up for me!

  29. 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.

  30. 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


    • Stephanie

      I would love to know how to create a room resource! So difficult to figure out on Outlook with Office 365.

  31. Michael

    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!

  32. 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 🙂

    • Steve Mordue - CEO

      The storage limit of Shared Mailbox without a license is 5 GB. However, if the storage is over 5 GB, then it’s required to assign an Exchange Online license to this Shared Mailbox. The storage limit of a Shared Mailbox with a license is 25 GB.


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