This is the 4940th most frequent Polish word.
poczty
"Mail" or "post offices" (plural form of "poczta").
In this sentence, 'poczty' is used in the genitive case referring to the 'post office' where one intends to go.
Muszę iść do poczty, żeby wysłać list.
I need to go to the post office to send a letter.
Here, 'poczty' is again genitive case, denoting association or employment with the postal service.
Mój dziadek był pracownikiem poczty.
My grandfather was an employee of the post office.
In this example, 'poczty' is genitive case, indicating possession or location relevant to the facility.