Send email from an alias in Outlook

Jan Jansen has the address jan@contoso.com, but customers know him as j.jansen@contoso.com. Mail to that second address simply arrives in his inbox. When he sends a message himself, Exchange Online rewrites the sender address to his primary address by default, and that is what the recipient sees.

Exchange Online can also let users send from such a second address, an alias. In this blog post you read how to turn on sending from aliases in Exchange Online, add an alias to a user and choose that alias as the sender in Outlook on the web. You also read what plus addressing is and why you cannot send from it.

What is sending from an alias?

An alias is an extra email address on a user’s mailbox. Mail to the alias arrives in the same inbox as mail to the primary address. According to Microsoft you can give a user up to 400 aliases, without an extra license or cost (Add another email alias for a user). If several people have to handle the mail on one address, such as support@contoso.com, Microsoft recommends a shared mailbox instead of an alias.

By default, Exchange Online rewrites an alias on messages to the primary address. The organization setting SendFromAliasEnabled of Set-OrganizationConfig turns that rewriting off. Outlook clients that support it then let users send from an alias and reply to an alias.

What do you need?

• An Exchange Online mailbox for the user, with a license: without a license you do not see the option to add an alias.
• An Exchange admin role, such as Exchange Administrator, to manage aliases.
• Permissions on the Set-OrganizationConfig cmdlet to change the organization setting.
• The ExchangeOnlineManagement module, if you work with PowerShell.
• A domain that has been added to your Microsoft 365 organization, for the address of the alias.

Turn on sending from aliases in Exchange Online

The setting applies to the whole organization. Users without a newer Outlook client can notice something too, because it acts on all messages a mailbox sends and receives. So let users know that this is coming. Microsoft Learn describes the setting as a parameter of Set-OrganizationConfig; that is why the PowerShell route is shown here.

1. Connect to Exchange Online PowerShell with your admin account.
2. Set SendFromAliasEnabled to $true.
3. Disconnect when you are done.

This block runs the three steps:

# Connect to Exchange Online with an admin account
Connect-ExchangeOnline -UserPrincipalName admin@contoso.onmicrosoft.com

# Stop rewriting aliases to the primary address, so users can send from an alias
Set-OrganizationConfig -SendFromAliasEnabled $true

# Close the session
Disconnect-ExchangeOnline

With $false you set the setting back to its default value.

Add an alias to a user

Microsoft describes adding an alias as a task for the administrator, in the Microsoft 365 admin center.

1. Navigate to Users > Active users and select the user.
2. Under Aliases, click Manage username and email.
3. In the Username field, enter the first part of the alias, for example “j.jansen”, choose the domain and click Add.
4. Click Save changes.

In the screenshots, the alias support@ is a personal alias of one user; for an address that several people handle, you use a shared mailbox.

It can take up to 24 hours before a new alias is updated everywhere.

💡 If the user is synchronized from an on-premises Active Directory, you add the alias there, in the proxyAddresses attribute with the prefix smtp: in lowercase. Then wait until the change has been synchronized to Microsoft Entra ID.

Choose the alias as the sender in Outlook on the web

When sending from aliases is turned on and the feature is available in Outlook on the web, the user gets a list with a checkbox per alias in the Outlook on the web settings. An alias they select there can be chosen in the From field of a new message.

1. Open the Outlook on the web settings and find the list of checkboxes for your aliases.
2. Select the alias and save the setting.

3. Create a new message and choose the alias in the From field.
4. Write the message and send it.

Plus addressing: receive, but not send

Plus addressing looks like an alias, but works only for receiving. A user puts a plus sign and a label after the first part of their address themselves, such as jansen+newsletter@contoso.com. Exchange Online delivers that message to jansen@contoso.com. Nobody has to create such an address, and with an inbox rule on the receiving address the user sorts such messages automatically.

Plus addressing is on by default in Exchange Online. A plus address is not an alias on the mailbox: the user cannot send from it, and Outlook does not show it as their name in To or CC.

Turn off plus addressing

If you do not want it, you turn it off for the whole organization.

1. In the Exchange admin center, navigate to Settings > Mail flow.
2. Select Turn off plus addressing for your organization and click Save.

In the screenshot the checkbox is selected, so plus addressing is off there.

With PowerShell you do the same with the DisablePlusAddressInRecipients parameter:

# Turn off plus addressing for the whole organization
Set-OrganizationConfig -DisablePlusAddressInRecipients $true

User experience

When a user sends a message from an alias, Exchange Online no longer rewrites the alias to the primary address. Because the address is no longer rewritten, the recipient sees the alias as the sender.

When replying, the sender address depends on the client. Outlook on the web replies from the alias the message arrived on. According to Microsoft, Outlook for desktop replies from the primary address, although support differs per client and version; Outlook clients that support sending from aliases can also reply from the alias. Tell users this, so they know which address the recipient sees.

Wrapping up

With one organization setting, an alias per user and a checkbox in Outlook on the web, employees can send email from a recognizable address in Outlook on the web, and in other Outlook clients that support it, without an extra mailbox or license. Plus addressing complements that for addresses on which you only want to receive.

📚 Read more in Add another email alias for a user and Plus Addressing in Exchange Online.