Severus hated mail time.
This was not because (contrary to popular belief) he was a completely anti-social bastard who received no mail and was jealous. He received Potions journals at least twice a week, as well as requests for complicated and rare potions.
Nor was it that he had had a traumatic encounter with an owl at a young age. Or even that the high pitched squealing of excited first years filled with lollies from home hurt his ears – indeed, he found it a rather homely sound, due to it's similarity to the sound his students made when he gave them a pop-quiz.
No, what Severus hated were the Recipient Unspecified Marketing Owls.
It had been bad enough when he was a student, and the owls were randomised, dropping their mail onto every third or forth plate. Then, a letter reading; "send us 10 Galleons and we'll send you a tube of charmed lipstick guaranteed to catch that elusive boy," could be shrugged off as just random. Then, he had been able to at least pretend that the laughter was with him, not at him.
But RUMOs were more directed, these days. The owls were spelled to deliver their letters to only likely looking candidates.
So when Severus received three different owls advertising hair cleaning products in one morning, it could not be laughed off as a mistake.
When owls detoured to drop free lipstick samples on his head, there was no error or misdirection.
And when he received howlers that suggested that he should consider brushing his teeth more often; it had to be that his mouthwash potion had expired.
But, naturally, that didn't save the Weasley twins from a detention or ten.