What you describe is an unfortunate result of Spam proliferation. Spam control systems use databases, algorithms and users' feedbacks. Sometimes even legitimate domain names get a bad reputation due to numerous e-mail users complaints worldwide. This happens for example if a company uses an obsolete mailing list.
As a bluewin webmail user you can signal this e-mail as non-spam. You can also ask the domain name owner to contact Swisscom (only for domain owners):