Sending, receiving, and organizing email in Outlook.com
Hello,
I have similar problem, I am the admin for Microsoft 365 at my organization.
Some users needs to send occasionally emails from their alias addresses.
I can't see any why to do it in Outlook Web (Works fine in Outlook 2019 app).
The instruction I could find are to go to settings, Compose and reply, Addresses to send from and choose the alias email addresses you want to use. But there is no option called Addresses to send from.