In short: since 7 October 2026 Exchange Online lets users send and reply from any alias of their mailbox, not only from the primary address. It is enabled with a single tenant-wide setting and works in Outlook on the web, desktop and mobile. Before turning it on, however, it is worth checking mail rules, journaling, message trace, shared mailboxes and the authentication of secondary domains.
What changes
In Exchange Online a mailbox can have several addresses: the primary one and one or more aliases (proxy or secondary addresses), for example info@, an old address kept after a name change, or the address on a second group domain. Until now aliases could only receive: every reply was sent from the primary address. To really write from another address, people used shared mailboxes or distribution groups with send permissions.
With the “Sending from Aliases” feature, long in public preview and now generally available, users can send from any alias directly in Outlook, reply from the alias the message was addressed to and choose which aliases to display in supported clients. For anyone managing Microsoft 365 it is a chance to remove mailboxes and groups that only existed as a workaround.
How to enable it
The setting applies to the whole tenant and is enabled by an Exchange administrator, in two equivalent ways: in the Exchange admin center, under Settings → Mail flow, by turning on “Sending from Aliases”; or in Exchange Online PowerShell with Set-OrganizationConfig -SendFromAliasEnabled $true. Microsoft states that it may take up to 60 minutes for the change to take effect.
Individual user aliases are managed as usual in the Microsoft 365 admin center. If an entire domain must not send (or must not receive), it can be set as “Receive-only” or “Send-only” with the SendingFromDomainDisabled and SendingToDomainDisabled parameters of the Set-AcceptedDomain cmdlet. Finer restrictions, per user or per alias, have to be built with mail flow rules or internal policies.
What users see
| Client | How to choose the alias |
|---|---|
| Outlook on the web | Settings → Compose: choose which aliases to show and select them |
| Outlook desktop (Windows and Mac) | Drop-down menu in the “From” field, or type the alias manually |
| Outlook mobile | Tap the “From” field and pick from the available aliases |
In all clients, replies are automatically sent from the alias the message was addressed to.
Before enabling it: what to check
Microsoft itself warns that the feature is a significant shift in Exchange Online behaviour and that some edge cases may still emerge. These are the points to verify:
- 1Rules that look for a specific address — mail flow rules, journaling, hygiene and routing rules written against the primary address may not match messages sent from an alias, and so not apply to part of the mail.
- 2Message trace — a search on the primary address does not return messages sent from an alias: to trace them, use the alias. Support staff need to know this, otherwise a message “was never sent” when in fact it went out.
- 3Hybrid environments — the feature applies only to mailboxes hosted in Exchange Online. With on-premises servers still running, aliases may be rewritten by those servers and out-of-office replies may be sent from the routing address in the form
tenantname.mail.onmicrosoft.cominstead of the company domain. - 4Shared mailboxes — sending from aliases works only in Outlook on the web, opening the mailbox with “Open another mailbox”. It is not supported in the Outlook client.
- 5A changing “From” field — if Outlook had been configured with addresses or display names different from those of the mailbox, after activation sent messages may show a different sender than before.
- 6Authentication of secondary domains — an alias on another domain sends mail on behalf of that domain. SPF, DKIM signing and DMARC of that domain must be aligned with Exchange Online, otherwise with a strict DMARC policy messages risk quarantine or rejection. This point is not in the Microsoft announcement: it is the check we add, and the one we follow with DMARC monitoring.
What is still missing
General availability covers the core functionality. Microsoft says it is investigating, without committing to deliver them, three extensions: a separate display name for each alias, additional filtering and default-alias controls, and calendar support. So today the display name is the same for every alias of the mailbox, and the calendar is not yet covered by the feature.
How we handle it
Before enabling the feature on the tenants we manage, we run a round of checks: the list of aliases and domains in use, mail flow and journaling rules that depend on the primary address, shared mailboxes used only to write from another address, and the SPF, DKIM and DMARC records of every domain that will send. Only then do we enable it, test sending from the clients the company actually uses and show users where to find the alias. If the company archives its mail, we also check that email archiving keeps capturing messages sent from aliases.
AtWorkStudio has been operating from Piacenza since 2000. We are certified ISO/IEC 27001, 27017, 27018 and ISO 9001, ACN (Italian National Cybersecurity Agency) qualified for cloud services, members of Clusit (Italian Association for Information Security) and affiliated to Confindustria Piacenza in the RICT cluster.
Sources
- Microsoft Exchange Team Blog — “Sending From Email Aliases – General Availability”, 7 October 2026
- Microsoft Learn — documentation of the Set-OrganizationConfig (SendFromAliasEnabled parameter) and Set-AcceptedDomain cmdlets
- Microsoft Learn — “Add or remove email addresses for a mailbox in Exchange Online”