When setting up a POP client, it's required to use your main full business email address as the username in the POP client's settings. To send as your main business email address, it would also be entered into the Email Address field in the POP client's settings.

However, if you'd prefer to send as a business email alias rather than the main business email address, enter the business email alias into the Email Address field.

Send business email as an alias

1. Follow the initial steps to set up your POP client.
2. When you get to the settings page to enter the email address, username, and password, enter your business email alias into the Email Address field.
   Important: You will still enter your main full business email address into the User Name field.
   
3. In Outlook, click the More Settings button.
   
4. On the General tab, ensure that your business email alias is entered into the Mail Account field.
   
5. Click OK.
6. Continue with the POP setup.

If you wish to send as the main business email address as well as the business email alias, you will need to set up an additional mail account in the POP client. The main business email address would be entered into the Email Address field and into the Mail Account field on the General tab in More Settings.

Once the setup for both are complete, both accounts will appear in the Email Accounts screen. This will allow a send as option for both accounts.