If you're like me - you most likely have several email accounts setup within Microsoft Outlook, with one of those accounts being listed as the default. Recently, the responses I was getting to my email were in response to an account that was not my default account. I didn't make much light of this, as emails to my wife were still being replied to my default account. But, after a couple of days of this error I was getting annoyed. I checked my settings, and the right account was listed as my default. I even did some tests emails and explicitly clicked on the option to send the email from my default account, and the emails still showed up as being sent from another account. I started doing a search on Google and quickly came across this article describing the same problem that I had. Basically, if for any reason, your default "send to" account encounters any problems sending out the email - it won't tell you about the problem, but will just send the email from one of the other accounts you have setup - doh! Why it is designed this way I have no idea - you'd *think* it would at least tell you "Problem sending from account x, would you like us to send from a different account instead?".
Turns out that my problem had to do with my outgoing email server. I had recently visited my parents in Miami over Thanksgiving and I had to switch my outgoing email server - due to restrictions from their DSL provider. When I cam back home I switched back my outgoing email server to the correct one, but forget to set the authentication properly.
A feature I would *really* love to see in an upcoming version of Outlook is someway to specify an overriding outgoing email server for all your email accounts. Ex. Outlook would retain your default outgoing email server for all your email accounts, but would override them with a specificied server if you flip a setting. This would be extremely usefuly for those of us that travel to different networks. Changing my outgoing email server, for every of my accounts, each time I visit my parents, in-laws, or am at a hotel, is a PITA.