Send from alias (SMTP proxy address) in Exchange Online (Microsoft 365)

An Exchange mailbox can be assigned several additional SMTP addresses, known as proxy addresses (aliases). These addresses allow the user to receive e-mail sent to various SMTP addresses. Exchange uses the user’s primary SMTP address when sending e-mail. Exchange Online (Microsoft 365) introduces the ability to send e-mail from an additional SMTP address (alias), which is assigned to a user’s mailbox.

Earlier in Exchange, you could use the Send As feature when you needed to send mail on behalf of the SMTP address of another user, group, or shared mailbox.

Sending on behalf of aliases is disabled by default in Exchange Online. To enable it:

  1. Connect to Exchange Online by using the EXOv2 PowerShell module:
  2. Verify whether your Microsoft 365 tenant allows sending on behalf of aliases: Get-OrganizationConfig| ft SendFromAliasEnabledGet-OrganizationConfig SendFromAliasEnabled
  3. in this instance SendFromAliasEnabled = False, To enable sending using proxy addresses: Set-OrganizationConfig -SendFromAliasEnabled $True
    You can also enable this option from Exchange Admin Center -> Settings -> Mail Flow -> Enable sending by alias.Enable sending email as an alias in Microsoft 365
  4. You can now use Outlook or Outlook for Web to send e-mail from users’ alternate SMTP addresses.

Add an additional SMTP alias for the user via EAC (Mailbox -> Select User -> Email Addresses -> Manage Email Address Types -> Add an Additional SMTP Address) or by using PowerShell:
Set-Mailbox max.wolff -EmailAddresses @{add="[email protected]"}
Add a user's email alias in Microsoft 365

A list of all SMTP addresses assigned to a user mailbox can be displayed like this:

Get-Mailbox max.wolff | fl EmailAddresses, PrimarySmtpAddress

Get-Mailbox Show All Email Addresses

You can now send e-mail from any additional SMTP address.

If you are using Outlook for web, open your mailbox settings (Settings -> Mail -> compose and answer, find out address to send section. Here you can see additional SMTP addresses that will be available in From field when you send an e-mail from Outlook.

Check off the assigned nicknames you want to use.

Select mailbox SMTP aliases to show in Outlook "From"

Create a new e-mail message and enable it show from Option. Now you can choose from which SMTP address you want to send e-mail.

Show 'From' filed in Oltuk

Click the From field, select an SMTP address from the list, and send an e-mail.

Select a mailbox alias to send from,

When you locate a message in the Exchange Online log, it will be displayed with an alias address in the From field.

The Send on Behalf of Aliases feature only works for mailboxes in Exchange Online and is not available for on-premises Exchange servers.

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