Exchange Online makes sending from aliases generally available

On October 7, 2026, the Exchange Online team announced general availability of Sending from Aliases. The feature was previously in public preview. With it, users can send from any alias (proxy address) on their mailbox, not just the primary SMTP address. Microsoft notes that aliases could previously only receive mail. Every outgoing message used the primary address, and organizations relied on workarounds such as shared mailboxes or distribution groups.

How admins enable sending from aliases

The feature is turned on per tenant. Microsoft gives two routes:

• PowerShell: Set-OrganizationConfig -SendFromAliasEnabled $True
• Exchange admin center: Settings → Mail Flow → Turn On Sending from Aliases

Microsoft says the change can take up to 60 minutes to apply. Aliases are still managed in the Microsoft 365 admin center. A whole domain can be set to send-only or receive-only with the SendingFromDomainDisabled and SendingToDomainDisabled parameters of Set-AcceptedDomain. Finer-grained restrictions need mail flow rules or organizational policy.

Users pick the alias from the From field in Outlook on the web, Outlook for Windows and Mac, and Outlook Mobile. Replies automatically go out from the alias that the original message was addressed to.

Known gaps Microsoft lists

The announcement lists several behavior changes:

• Rules that match on specific addresses, including hygiene, journaling and mail flow rules, may not act on messages sent from an alias.
• Message Trace searches on the primary address no longer return mail sent from an alias. Admins have to query the alias itself.
• The feature covers Exchange Online mailboxes only. In hybrid setups, automatic replies can come from the tenant's mail.<tenant>.onmicrosoft.com routing address.
• For shared mailboxes, alias sending works only in Outlook on the web, and only when opened via "Open another mailbox". The Outlook desktop and mobile apps don't support it for shared mailboxes.

Microsoft says it is investigating per-alias display names, calendar support and extra default controls, without committing to them.

What it means for authentication

This part is our analysis, not Microsoft's. The visible From address is the domain that DMARC evaluates. Once alias sending is on, a mailbox can send under any domain it holds an alias for, not just the primary one. Mail from each of those domains has to pass DMARC on its own, which means SPF or DKIM must align with that domain. If an alias domain has no DKIM signing set up, its mail can fail DMARC, and receivers that enforce the domain's policy may junk or reject it. Outlook.com's rules for bulk senders are in our Outlook sender requirements. Before enabling the setting, check every alias domain with our DMARC checker, or set unused domains to receive-only.