Custom Login Url without port 8443

Hi friends of Plesk,

i have a little problem.

We want change the logon url.

an example:

standard login url ist: mydomain.dom:8443

now we want to login into plesk with the domain only:

mydomain.dom (without port 8443)

netcup use ist at: webhostingcontrolpanel.de

we want the same.

our system: debian 7.9 with plesk 12.5 web host edition

any ideas? thanks for your answer ;-)
greetings frundaa