https://webmail.uni-koeln.de/login.php?url=https%3A%2Fwebmail.uni-koeln.de%2Fimp%2F%3F_t%3D1521504110&_h=plChwQeFwrOtvBOgUjMWiV0h7i4&horde_logout_token=VU6BQlLdJcMoxLgoTTgymtE

This URL has not been tested yet.