Last reviewed on August 12, 2015   —  17 Comments

Microsoft Office 365 Change From domainAn Office 365 user was trying to make Outlook use his vanity domain as the From address instead of the Office 365 default domain (

This is not something that is controlled from Outlook, its set on the server. While you can have multiple addresses assigned to your mailbox (and receive mail sent to those addresses) Outlook always uses the default SMTP address assigned to the Exchange account as the address for replies or new messages.

In a local Exchange server, changing it is as easy as the administrator logging into the server and changing a mailbox policy. It usually takes longer to log in than it does to make the change.

In Office 365, the administrator can log in and change individual users or use a cmdlet to change the domain used by all users. If the account you want to change is the administrator account (common among SOHO users), you either need to make a new admin account and log in with it to reassign the primary email address of the first account or use the set-mailbox cmdlet.

If you choose to create a second administrator account, you do not need to assign a mailbox to it (therefore, no license is needed). It won’t be used for receiving email and will not be using Office 365 outside of the administration panel. If you are purchasing more than one account, you can (and probably should) make at least one of the other accounts an administrator. Do not delete the account, especially if you have already set up the other online services.

These steps assume you’ve already added the domain to the online account and your account has administrator permissions.

  1. Login into
  2. Click users & groups
  3. Double click on the user name whose address you want to change
  4. Click details
    Change the domain name for a user
  5. Select a different domain from the domain name list for the User name.
  6. Click Save

Using the set-mailbox cmdlet takes a little longer but will be faster if there are a large number of addresses to change, since you can use a CSV to update the addresses.

  1. You’ll need to configure PowerShell to connect over the Internet. If you don’t use Windows 7 or Windows 2008 R2, you may need to uninstall PowerShell and install the current version. See Install and Configure Windows PowerShell – if using Windows7 or 2008 R2, skip to Step 4 in these instructions.
  2. Establish a connection to the online server. See Connect Windows PowerShell to the Service for details.
  3. Run the Set-Mailbox cmdlets for the users that need changed from addresses to your domain addresses. The cmdlet is formatted like this:
    Set-Mailbox diane -EmailAddresses

For more information and instructions to change multiple users using the cmdlet, see
Change a User’s Primary E-mail Address

The easy way to avoid this hassle is to create the Office 365 account, add your vanity domain (and set it as the default domain) then add users and mailboxes, however, many people want to try Office365 before they move their existing domain to the service and use the initial administrator account for email during the trial.

Fortunately, you can change the default domain for new accounts in the portal or with a cmdlet (cmdlet is only available in the on-premises Exchange 2013).

Set the Default Domain for New Accounts

You can set the default domain for new users in the Office 365 Admin Center.

Login to the portal, click Domains. Select the domain that you want to set as default then click the Set as default link on the right.

This screenshot is from an E account; Business accounts are similar but may be missing the left bar.
Change the default domain

If you prefer to use a cmdlet, you’ll use the Set-AcceptedDomain cmdlet (available in on-premises only).

Set-AcceptedDomain -Identity -MakeDefault $true

Discuss in our community


  1. martin says

    I tried to follow this, Office 365 user but i am getting an error message
    The proxy address "SMTP:xxxxx@yyyyy" is already being used by xxxxxx_561b7d978b". Please choose another proxy address.
    any help would be really appreciated


    • Diane Poremsky says

      You should only get this error is the alias is already in user with another account. You can have multiple uses of the same alias as long as they are in different domains. For example, I have two domains hosted in my Office 365 hosting account and have diane@ set up in both. The one has numbers tacked on the end, like in your example.

  2. Scott says

    Hi Diane, I see there are many related posts but I cant find the exact one for my situation. I have an office 365 account and have set up two domains and My user's primary email address is however there are times I want to SEND FROM from outlook desktop application. How can I do this? Thanks, Scott

  3. Tim says

    Hi, Diane, we've been on O365 since the middle of last year and even though we added our vanity domain and have manually set our users' primary SMTP: addresses to use the vanity domain, our new users still come up with and we have to manually change those as well. Is there a default setting we can change so that all new user accounts set primary SMTP: to the vanity domain?


    • Diane PoremskyDiane Poremsky says

      Yes, you can. In the Admin center, under Domains, select the vanity domain and click Set as default. (I'll add a screenshot to this page.)

  4. Gigi Axline says

    wow! great website! my quick question is...if i have a user set up as then add another domain and set that as the new default, which email address will the portal accept as the login/username?

    • Diane PoremskyDiane Poremsky says

      It depends. Office365 will use the default address ( but on-premises exchange might accept any address on the mailbox as the log in.

  5. W says

    Hi Diane,

    My company has recently purchased a new domain and would like to use the new domains email address. We currently have Office 365 with DirSync for on-premises user passwords and Active Directory sync. I'm not sure how to set this up so that on-premises and office 365 will use the new domain email address as the default (for sending email), but the old domain email address will need to still be used to receive emails.

    Any assistance with this will be greatly appreciated.

    • Diane PoremskyDiane Poremsky says

      On the office365 side, you'll add the new domain then add an address to each user for the new domain and set it as default, leaving the old address on the accounts as a secondary address. Obviously, with a lot of users, you'll want to use PowerShell. I'm not sure what you need to do on the on-prem side to keep it from breaking dirsync.

  6. Rob Copeland says

    Hi Diane - I have a customer who has offices in two different states, one domain, (example) -- the main office ( uses godaddy webmail. I've created a subdomain ( and configured that subdomain for Office 365.
    The customer using wants to send / recieve emails as "" -- can I achieve this using aliases in 365?


    Rob Copeland

    • Diane PoremskyDiane Poremsky says

      I'm not sure - did you try adding aliases for the bare domain? You'll need to set up forwarding accounts at godaddy so the messages don't bounce.

  7. David says

    Hi Diane,
    I have a user with office365 account, and thus a primary address created was, now the user wants to use a new address: Both and domains exist in the same office365 account. So i have created a new email "" for the and ticked the box, use as default reply address. The idea was that any new emails and replies coming into the user's account (via or will be replied showing "" email address as the source/reply address, however this is not the case. The replies and any new emails still go out showing as the source.
    How can I change this to show as source of the replying/new email?

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