webmail for email adress doesn't work --> "not found"-message

[AhugaBar]

When I click the icon "open webmail for this e-mail adress..." I get the error:

Not Found
The requested URL /imp/login.php was not found on this server.
Apache/2.2.9 (Debian) PHP/5.2.6-1+lenny16 with Suhosin-Patch Server at webmail.web48.ch Port 81

Maybe this is a configuration problem.

Do you have any idea?

Thanks for any help.