From and aesthetic point of view, it is best for young women to wear a skirt or a dress, with some nice cleavage as well - and for the men, a suit.
The writer of the email added, as if as an afterthought, "Of course, ladies, this advice is not obligatory". The "sincerest apologies" come after the suggestion caused an outcry on social media.
The university issued a statement via Facebook and Twitter on Saturday, apologizing to all who received the message.
The post attracted more than 600 comments, many written by incensed students.
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The ULB Confessions page also published a response it had received from a student: "No one has the right to tell you how you should feel in your skin".
'Nobody has the right to tell you how to dress.
"It goes without saying that the instructions linked to the dress of young female graduates are as far removed from as they are contrary to the values defended daily by ULB and its faculty". "Nobody has the right to tell you how to play your role as a woman", they continued.
According to Marco Schetgen, the medical faculty dean, it was a woman wrote the email, since no employees at the secretariat were men.
'No one has the right to take away this freedom that has been (and is still being) obtained with such difficulty'.
He confirmed it was "not a hoax", that the message had been sent out, adding it had shocked him too when he saw it.