noun
mailbox
B1
Briefkasten: mailbox or postbox. Masculine noun der Briefkasten. Plural: die Briefkästen (Umlaut plus -en). Declension uses die/den forms; dative plural den Briefkästen. Compound of Brief + Kasten. Plural forms change vowel (a→ä) and add -en. Used for letters and small parcels, usually at houses or on the street.
Examples
Der Postbote warf den Flyer in den Briefkasten, obwohl viele Leute schon Werbung ablehnten.
The postman threw the flyer into the mailbox, although many people already rejected advertising.
Der Briefkasten wird täglich geleert.
The mailbox is emptied daily.
Bitte steck den Brief in den Briefkasten.
Please put the letter in the mailbox.
Details
Mnemonics
Picture a red box on the street with a slot and the word 'BRIEFKASTEN' stamped on it.
Sounds a bit like 'brief' + 'casten' -> imagine 'brief' (letter) going into a 'cast' (box).
der = imagine a strong, masculine metal box with a little mustache sticker.
Notes
Commonly found on streets and at houses. 'Briefkasten' specifically refers to the physical receptacle for letters (not digital mail).