I have Outlook 2007 with a single IMAP mail account. I have a number of aliases configured for that account with my provider. Can I default Outlook to use one of those aliases for the "From" and "Reply-to" addresses when sending?
Depending on your ISP, you may be able to do the following:
Depending on how your ISPs SMTP server is setup, it may use this e-mail address as the from or reply-to address when sending mail.
Your mileage may vary.
In the ribbon, select
When the recipient will reply, it will reply to new address provided.