There's only one table in LS database where global settings are saved (as far as I can find): lime_settings_global. Don't you know your own database?
Well, here's is a commented screenshot, so you may see what I see.
www.hostingpics.net/viewer.php?id=370244LSsmtpusername.jpg
And excuse me if I'm blind, because I see no field corresponding my smtpuser value...
EDIT:
Ok, I'm blind. There's a second page at the bottom of phpmyadmin.
So yes, there's a emailsmtpuser there. And the "\" is correctly saved.
So my issue is elsewhere...
I'll be back when I've figured where my setup is wrong.