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I have the exact same situation here. I have many "logical" email addresses that all forward to my "real" email account. The good news is that Outlook does have a way to control what accounts are checked, and when. It's not obvious, and not terribly simple, but it is there.
First let me explain the situation in a little more detail.
Let's assume that your "real" email address is "firstname.lastname@example.org". That's the account that really and truly sends, and receives, all of your email.
Here's how that account might be configured in Outlook:
Now, if you own the domain "example.com", you can define as many email addresses on that domain as you like, and have them all automatically forward to your "real" account. For example you might create "email@example.com", and use that email address as your Amazon.com contact address. When Amazon sends email to you at "firstname.lastname@example.org", it's automatically forwarded to "email@example.com". When you download your email (through your "firstname.lastname@example.org" account), you'll see the "email@example.com" address in the "To:" line of those messages, so you can see what email address was used. It's a nice way to track who's using your email address and how.
The nice thing is that no re-configuration is needed in Outlook. Email forwarded to your account simply shows up like any other email.
But so far, every email you send will come from "firstname.lastname@example.org". What if you want to send email From: "email@example.com"? Then some Outlook reconfiguration is needed. To do this, you'll create a second, additional email account in Outlook:
Note that there are only two changes:
Note also the things that didn't change: your mail servers, of course, and the User Name and Password. It's the User Name and Password that really identify you and your account to your mail server. "Your Name", and "E-mail Address" in the configuration is only used to fill in the "From:" field on email you send using this account - exactly what we wanted to change. Everything else remains the same.
At this point it's also nice to go into the More Settings dialog and change the name of this account:
Now, when you compose or reply to an email message, the Accounts dropdown will list "firstname.lastname@example.org" in addition to the previous, default account. To send from this account, select is in the Accounts dropdown before pressing Send:
Now notice what happens when you press Send/Receive ... Outlook sends mail from each account, but then it checks mail from each account. Remember, it's the same "real" account as defined not by the email address, but by the User Name and Password, that are defined the same for both. So the same account gets checked twice for new mail.
That seems a waste of time. Let's fix it.
On the Tools menu, select Options and then click on the Mail Setup tab. Now click on the Send/Receive button. In the resulting dialog there should be one Group Name defined, "All Accounts". Make sure that is selected, and click on the Edit button. This long journey of clicks and selection should have you looking at something similar to this:
This dialog allows you to control which accounts are included in the Send/Receive operation - exactly what we set out to do. In our example, we'll click on the email@example.com item on the left, and then uncheck Receive mail items:
(You can OK your way back out at this point.)
Now this account will no longer be included in the default Send/Receive action. All email will be downloaded using the default account, and you can send using this other email address by selecting it when you send.