Historically, Exchange has used a user’s primary SMTP address as the From address when sending messages. Other SMTP addresses assigned to a user (e.g., proxy addresses, also known as aliases) were mainly intended for receiving messages. Even when an email client tries to use an alias for the From address, that value is overwritten with the user’s primary SMTP address when the message is sent.
Today, business operations are much more challenging and complex, and activities such as mergers and acquisitions, rebranding, and other such changes have created the need for multiple identities and SMTP domains to be managed by an organization. To address these challenges, we started a journey toward making aliases first-class addresses in Exchange Online. We are excited to announce that we’ve reached the first milestone of this journey. In the past, those wanting to send from aliases had a few options. They could use the SMTP AUTH client submission protocol, which didn’t rewrite the From addresses. Shared mailboxes could be used, but that meant another identity and another Inbox, as well.
To eliminate the need for these suboptimal solutions, we have introduced new capabilities in Exchange Online that enable Outlook clients to use and preserve aliases and to display the original alias used to send the message. This is accomplished by no longer replacing aliases during the sending or delivery of messages in Exchange Online.
The new capabilities are now available in Public Preview for Outlook on the Web and Outlook for iOS and Android. You can access the Preview using the SendFromAliasEnabled parameter of the Set-OrganizationConfig cmdlet. The setting enables the new functionality for all Exchange Online mailboxes in the organization. Note: it might take up to 60 minutes for this change to take effect in your tenant.
This feature is in Preview because we have made fundamental changes throughout the email pipeline. There are known compatibility issues with some features that assume the user’s primary SMTP address will always be used. These known issues are listed below. We will work to the update the known issues list in this post periodically.
This is the first iteration of our support for aliases. We do have plans for additional functionality, but we want to hear from customers about what they want. Client support Support for sending from aliases has been added to Outlook on the web and Outlook for iOS and Android. Mobile clients allow users to enter aliases in the From field and those will be saved for future use. Support for Outlook for Windows was enabled at Monthly Channel 100% starting 1/17/23. We will update here when the feature advances to other channels. Desktop clients will display a list of enabled aliases in the From field, and messages sent from an alias will have that address preserved.
Aliases will also be preserved when messages are addressed to them. If a user replies to a message that was sent to their alias, their reply will come from the alias by default. Outlook on the web The From drop-down now contains a list of available aliases:
This list of aliases can be customized by the user in Settings from the full list of aliases (proxy addresses) that are associated with their mailbox.
Outlook for iOS and Android Aliases can be entered into the From field. Previously used aliases will be saved and available via a dropdown list:
Outlook for Windows Support for aliases is on the way for Outlook for Windows. The From field will also support a customized list of aliases.
It’s possible to customize the list by clicking on Manage List…, which is the same as changing them on the Settings page in Outlook on the web.
Outlook for Mac support for this feature is planned (we will provide more information as it becomes available).
Known Issues This being a preview, we are aware of several known issues (updated August 2023):
For shared mailbox, send from alias feature works only with OWA when delegate opens it using “Open another mailbox” option. For Outlook client, send from alias feature is not supported for shared mailbox at all.
Similarly to shared mailbox mentioned above, send as alias feature does not work using Outlook for regular user mailboxes with “Send As” or “Full Mailbox” permissions.
Outlook for Windows currently shows the original email address instead of the alias if an internal user replies on an email. If you intend to use aliases where you will have replies from external parties and internal parties on the same email make sure to factor in this limitation.
Various types of rules in Exchange Online, such as hygiene or journaling rules that are configured to look for specific email addresses, may not match aliases, resulting in the rule not acting on those messages.
Multiple customers have reported issues with journaling rules not triggering messages with aliases.
Messages sent to aliases were rewritten to the primary SMTP address in the past. Complex routing configurations may rely on this behavior. When the sending from aliases feature is enabled, rewriting to the user’s primary SMTP address will stop, which could break routing. Customers have seen this when aliases with different domains are used
Forwarding/Redirecting using Inbox Rules sees the address being sent to resolved to the primary SMTP address while the Resent-From header shows the alias address used.
Different email addresses or display names may appear. Some companies have set up Outlook clients with aliases or display names that differ from the user’s primary email address and display name stored on the mailbox. When the sending from aliases feature is enabled, it may cause a change in behavior for what shows up in sent messages’ From field.
When using the user’s primary SMTP address in a Message Trace query, the results do not include messages sent using an alias. To trace messages sent to or from an alias, you need to use the alias in your query. This is less of a known issue and more about highlighting the change to existing behavior.
This feature is for Exchange Online-hosted mailboxes only. Messages to and from on-premises can be subject to rewriting the aliases on those servers.
Support in Outlook for Mac has not been added which will affect the preservation of aliases used in email threads
To provide feedback on the Preview (such as requests for additional features or functionality) we have set up an email to send those to: aliases-feedback[AT]Microsoft[DOT]com. We will monitor these to determine what functionality to invest resources into. Please note that we will not be individually replying to this feedback.
Outlook client feedback / features can also be filed (and voted on) on our new Feedback Portal. Please use the in-app support for Outlook Mobile issues, and regular support tickets can be opened for other versions of Outlook clients.
Here are some Feedback Portal items related to the aliases feature: