Send as alias using Outlook

Send as alias using Outlook

Hi,

I have two domains on my account. I know I can create aliases from one to another and I know I can send emails using webmail client from the created aliases. I want to do the same using Outlook 2010 but just simply changing from field to alias email address doesn't work. I get error code 551. Is there a way to accomplish this without setting the account type as IMAP because I want to be able to use POP to download messages from the server permanently.

Thanks and regards,
Sinan A.