Etiquette for “selling oneself” for an advertised PhD position

I would like to ask you for advice about the etiquette at continental European universities for obtaining an advertised PhD position, whose applications should be submitted via an online system. Since, during my period in industry, I fully realised the importance of knowing the “hiring manager” when one is interested in a position, I was thinking of sending an email to the professor to sponsor my application. I would like to ask you if this is considered an acceptable practice.

I should also remark that I have just completed a Master’s degree in this university. What has so far discouraged me from my intention is that this PhD ad specifies that applications by email are not considered – which is however not the same that what I would do; I would just like to send an email saying, more or less, that I exist.