Hidden Account in Outlook 2010

You can delete the account so long as it is not your primary account. Go to Outlook, File, Accounts and delete the account.

If you wish to keep it for some reason but stop it from Send/Receive, go to Outlook, Send/Receive, Send/Receive Groups., Define Send/Receive Groups, All Accounts and click on Edit. Uncheck the account you do not want included in the F9 send/receive.

Both ideas above will work. ... Thinkpads_User

Was it originally the default account?

If so, you might switch the default to another account, reopen Outlook, then switch it back (checking for a glitch).   If it never was default, then this might not help.

Thanks tailoreddigital for your comments.
But this is not excactly the answer to my question.
The Problem is, that the account "andrea_schmocker@bluewin.ch" I want to get rid of does not exist under Outlook, File, Accounts. It also does not exist under Send/Receive Groups, All Accounts, as you can see on the screenshot below.
The only occasion the account is visible is when I press the F9-Key, as mentioned before.
So Outlook seem s to keep some secret place that is not shown anywhere in a configuration window.

Look in your user folder, in Documents, and then in the Outlook folder where Outlook 2010 keeps its PST files. Is there a PST file that belongs to andrea___  that could be deleted?  Do not delete any PST file you need, but I am wondering if somehow the account was isolated into its own file.

In the Outlook program folder, there is a program called SCANPST.EXE . Using a command prompt, run SCANPST against your PST files to look for errors. Close Outlook and back up the PST files first.  

.... Thinkpads_User

Thanks thinkpads_user for your comment

I have two PST-files on my System and both of them are used.
I did a SCANPST against both of them, errors were detected, I did a repair, but the problem remais unchanged.

Another thing to try, perhaps before registry edits, would be to re-create the email profile.

Close Outlook, securely back up the PST files, go to Control Panel, Mail and delete the Outlook Profile.

Restart the computer, go to Control Mail, Mail and create a new profile. Open Outlook and set up the accounts and then import the email into the new profile.

Plan the above carefully and allow time for the email to be imported in the last step.

... Thinkpads_User

Thanks a lot thinkpads_user!

The article you mentioned in fact did help!

Under the Key:
HKEY_CURRENT_USER\Software\Microsoft\Windows NT\CurrentVersion\Windows Messaging Subsystem\Profiles\Outlook\9375CFF0413111d3B88A00104B2A6676
I found a subkey that represented the unwanted account. After I deleted that subkey the mystery was solved.

Once again, thanks a lot!
gpsfsc

@gpsfsc - Thank you and thanks for the update. I am glad you got the problem solved with that link. My system is very different than yours so I was not sure. I was very happy to help you.

... Thinkpads_User

Just for the sake of completeness:
My system is running on Windows 7 Professional SP1 with Outlook 2010

Cheers
gpsfsc