Who sent this letter?

Your tax number. By post only, never by email or phone.The official wording A plain letter from the Bundeszentralamt für Steuern (Federal Central Tax Office) brings your tax identification number (IdNr / Steuer-ID) after your first Anmeldung. For data-protection reasons the number is only ever communicated by post — nobody legitimate will email or phone it to you. Keep the letter: your employer needs the number, and it stays yours for life. Source ↗

The TV-fee letter. Routine, not a scam, one per home.The official wording A letter from 'ARD ZDF Deutschlandradio Beitragsservice' follows your Anmeldung: the residents' registration office notifies the contribution service of every new registration, and the service then writes to clarify who pays the broadcasting fee for the dwelling. It is not a scam and not optional post — but only one person per dwelling pays. Source ↗

Your social-insurance number. Employers ask for it.The official wording When you are first insured through a job, the pension insurance's data office assigns your social-insurance number (Versicherungsnummer) and must inform you without delay, issuing a Versicherungsnummernachweis — the document that replaced the old paper Sozialversicherungsausweis. It contains only the number, your names and the issue date. Employers ask for the number; if the document is lost, a new one is issued via your Krankenkasse or the pension insurer. Source ↗

Your health card. Take it to every doctor.The official wording After you join a statutory Krankenkasse, your electronic health card (elektronische Gesundheitskarte, eGK) is sent to you by post — the fund may ask for a passport photo during registration. Carry the card whenever you visit a doctor or a hospital. Source ↗

Your bank card and PIN. Tell the PIN to nobody.The official wording After your account is opened, the bank sends you your Girocard and your PIN — and usually a confirmation of receipt by post or email right after you apply. Memorise the PIN and share it with no one; the bank itself will never ask you to tell it. Source ↗

The PIN letter for your permit. It looks disposable. Keep it.The official wording When you apply for an electronic residence permit (eAT) — or a German ID card — you receive a PIN letter for the card's online-ID function. Under its two scratch fields sit a five-digit one-time PIN and a ten-digit unblocking key (PUK). It looks disposable; it is not: keep it for as long as the card is valid. Source ↗

Your local tax office. The Steuernummer on it is not your Steuer-ID.The official wording A letter from your local Finanzamt carries a Steuernummer, and that is not the same number as the Steuer-ID. The Steuer-ID comes once from the Bundeszentralamt für Steuern, and a person may only ever hold one of them. A Steuernummer is the file number the local office uses for you, and it can change when you move or when your situation does. Source ↗

The Familienkasse has answered. The letter says yes or no.The official wording Child benefit is decided by the Familienkasse and the decision arrives as a Bescheid, so the letter itself says whether the answer was yes or no. One date on it matters more than the rest: money is only paid backwards for the six months before the month your application arrived, so a late application loses the months before that. Source ↗

Your certificate of conduct. Keep it; it carries a date.The official wording A Führungszeugnis is the certificate about what the federal criminal register holds on you, and anyone from the age of 14 can ask for one. Where you asked for it in order to show it to an authority, the law sends it straight to that authority instead of to you — so a copy arriving in your own post means you asked for your own. Source ↗