A major complaint from people who configured Outlook.com accounts in Outlook is how the alias accounts are handled.
In Outlook.com, you can select one of the aliases as the "From" account, while in Outlook, all mail is sent from the default Outlook.com address.
It's not possible to send email using the Outlook.com account in Outlook and send it From one of the alias accounts. All email sent from Outlook will use the default Outlook.com address, which can be changed online.
Log into your Outlook.com email account and click the Gear icon on the right, then select More Mail Settings. Click Your Email Accounts to open the page where you manage your current aliases or create new aliases. The last option on the page is the default email address. This is the address Outlook uses when it sends email from your Outlook.com account.
Please note: the email addresses in the screenshots are used only for screenshots and testing.
I use Outlook 365 desktop. I have aliases on my Outlook accounts but they do not show up in the From dropdown box list. So it is painful sending from an alias as I have to use the Send from Other Email option. How can I get the aliases to appear or how to send from them easily. I tried the option to set up a POP account but failed!