Not sure which version you're using, but this works fine. Go into personas, add the new persona, hit apply, and then create a new email. The Account drop will show up. If you want to make the new persona the default one (in 6.0.x), then go into Tools->Account Settings, and on the E-mail tab, hit Set as Default.
If this isn't working, send some screenshots as to what you're doing. You shouldn't have to restart Outlook for this to work, but try that anyway. |