A popular request by Exchange account users is the ability to send from proxy addresses or secondary aliases on a mailbox. Outlook.com accounts have been able to send using these proxy addresses for some time, but the capability was not added to Office 365 business mailboxes at the same time.
I have an Office 365 Exchange subscription for myself and have 3 different email addresses assigned to my mailbox. I receive email from all addresses in OWA, but I can only send email from one of the email addresses. How can I setup the other 2 email addresses to be able to send email from them, and display them as the sender address?
This is now possible, if the Office 365 administrator enabled the capability to send from aliases using PowerShell.
Set-OrganizationConfig -SendFromAliasEnabled $True
If you are the administrator and want to see if proxy address support is enabled, use
Get-OrganizationConfig | Format-list SendFromAliasEnabled
When it is enabled for the organization, users will need to enable it in Outlook on the web's Settings > View all Outlook settings > Compose and Reply and enable the addresses they want to enable as a proxy address. Addresses that are not checked cannot be used to send email!
Once the addresses are enabled, Outlook on the web and Outlook mobile will list the proxy addresses in the From field when composing a message, just as it is in Outlook.com.
This screenshot is from Outlook on the web:
In Outlook desktop, the user will need to add the address to the From menu using the Other Email Address dialog the first time they send from it.
Once the address is used, it remains in the account list for future use.
When the recipient receives a message from an alias address, the From and Reply To field will show that address.
If you are using a version of Exchange server that does not support proxy addresses, you need to use a utility to send from the additional addresses on your mailbox.
Proxy Manager lets you send emails from Outlook using any alias (proxy) SMTP address with an arbitrary display name from your Exchange account, hosted or on-premises. There are no server components, everything is done on the client side - just install Proxy Manager, and you are ready to go! Select one of your proxy addresses and click Send. Outlook 2010, 2013, 2016 and 2019 are supported.
SmartReply 365 is an utility for Outlook desktop (Windows) users who have enabled the Microsoft feature to send emails from an alias in Office 365. This utility will automatically populate the proper From: address when you reply to or forward a message received as alias. In other words, if you get a message addressed to firstname.lastname@example.org and hit Reply(Reply All, Forward) button, the replied/forwarded message will have email@example.com in the From: field. The utility is an Outlook COM add-in.
Send Messages Using Additional Exchange Addresses - this page includes a list of utilities that can handle proxy addresses.