Using classic Outlook for Windows in business environments
Hello Jack,
Thank you for writing to us here in the Microsoft Community. I am a Microsoft consumer and Independent Advisors who cannot access accounts.
According to your message, I have learned that you need help sending emails with aliases in your Outlook application.
Follow the steps below to add aliases and check if the issue is resolved.
Log in to the web version of Outlook (Outlook.office.com).
When you're done, click the gear icon in the top right corner.
Click Send Email > Sync Email >> Manage or choose a preferred alias
Add a new email ID that you want to appear in the Outlook app. You can add more than one.
Restoring and restarting the Outlook app
Go to the Outlook mobile app > Settings.
Select Office 365/Microsoft 365 account.
Click Restore Account.
Click OK to restart the application.
Open the Outlook application again, try to send the email and select the alias you added.
Helpful Article: https://support.microsoft.com/en-us/topic/cannot-select-from-account-in-email-with-outlook-desktop-d5018eaa-5163-4c20-b332-618e206c2e1b
Thank you for your kind understanding.