Learn Hardcore Spanish (Latin America): La sucursal de correos cierra a las seis.

transitive: to close something Cierro <a class="border-b border-dotted border-blue-400 dark:border-blue-500 cursor-pointer text-inherit no-underline" href="/grammar/spanish-latin-america/articles/definite-articles">la puerta. = I close the door.
intransitive: to close / to shut / <a class="border-b border-dotted border-blue-400 dark:border-blue-500 cursor-pointer text-inherit no-underline" href="/grammar/spanish-latin-america/verbs/periphrastic/dejar-de">to stop operating La tienda cierra a las ocho. = The store closes at eight.

sucursal = branch
oficina = office
oficina de correos = post office
correo / correos = mail, postal service, or post office depending on context

Why is it de correos and not del correo?

In this sentence, de correos is a normal way to say of the postal service or post office branch.

Why not del correo?

del = de + el
But here Spanish commonly uses correos as the name of the service or institution, without el

So sucursal de correos is a set phrase in many contexts, similar to:

Also, correo in the singular often means mail or even email, so de correos helps make the institutional meaning clearer.

Is la sucursal de correos the same as la oficina de correos?