1000 years ago
When the 4 founders created Hogwarts they were the first wizards to ever use owl post. They would use owls specifically for sending out introductory letters to first year students. This was never a problem. The owls always got their letters delivered. Every first year student or potential student got their letter.
900 years later
Albus Dumbledore was called to the headmaster's office. He was told that he was going to be made deputy headmaster. Headmaster Dippet told him about a tradition that dates back to almost a 1000 years. No matter how long it takes, no matter how many owls are sent, every single first year student must get their Hogwarts letter. Dumbledore was made to swear an oath on his magic to see that this is done no matter what. This was never a problem for him. Every Student got his or her letter.
70 years later
Albus is in a rush. Getting things ready for the upcoming school year. Another year of having to deal with the Marauders and their feud with Snape. "Minnie can you come through please?"
"Yes, Albus." Minnie steps through the floo into the headmaster's office.
"Lemon Drop?"
"No thanks"
"How are things going with the letters? Has every letter been sent?"
"Yes Albus." Replies Minerva. "Every letter has been mailed. Problem is one student has not yet replied."
"Who?"
"Bebe."
"Yes, I know of this girl. Muggle born. Her parents has had trouble with her her whole life. Just keep sending the owls no matter how long it takes."
"Yes Albus."
25 years later
"Smarties" says Minerva to the gargoyles protecting the headmaster's office.
"Albus, I have a problem"
"What is it, Minnie?"
"One please I have begged you to stop calling me Minnie. My animal form is a cat. It looks bad if I have a mouse nickname."
"Okay sorry Minerva. What else is the problem"
"It's Bebe. I have spent almost 30 years trying to deliver her letter. She keeps escaping the owls."
"How bad is it?"
"She is under the impression that she's being chased. She's paranoid that "they" are following her. She has moved and changed her name several times. She even moved to Tokyo for a day"
"Just keep at it. Any new leads?"
"Yes. As you know, Hogwarts is almost impossible to use muggle products. Especially computers. I found a website that is so old that it can be used at the school, Myspace. I found this guy named Han and another named Sheldon talking on it. Han was telling him about this crazy girl that keeps talking about "they". I think I found her. I am stopping the owls and going myself to New York."
"Go ahead, Minerva. It is still 2 months before start of term. Don't spook her. Even though she is in her 40s, no Hogwarts letter in 1000 years has failed to be delivered. This will not be the first."
As Minerva is walking into the diner to find Bebe, a woman runs out of there screaming, "they found me. The damn owls found me again." After this Minvera gives up snaps her wand and says to her self "Fuck this shit. I give up trying to send letters. Maybe that Han person can give me a job."