This was a mystery film, whose mystery was eventually solved. My copy of the German version does not have a title sequence and there may be more missing at the start. I'm told that it had an English title Magic Dates. It ends with the word 'Fin' and then with 'Diamant Video' and 'Ende'. This, along with the presence of Jacky Arnal and Marie-Christine Chireix (Christine Glenne), indicated that it was a German release of a French film.
It is set some time in the 19th century, judging by the costumes. A blonde woman (the Eva of the Italian title - played by Eva Kleber) seems to be having an affair with a gentleman who is well off enough to employ a maid (Marie-Christine Chireix, as a blonde). There is some narrative by both Eva and her lover, as well as dialogue. Eva and the gentleman experiment with sex together, including looking at a book of pornographic prints during one of their sessions. The maid tries to seduce her master, but he is not susceptible as he is waiting for his lover. Together they watch the maid masturbating, and experiment with anal sex while doing so, and then join in to make a threesome. Then the gentleman's friend, Jacky Arnal, arrives and makes it a foursome, including a DP for Eva (apparently).
See also here.