Correo vs. correspondencia
The words 'correo' and 'correspondencia' both refer to items sent or delivered by postal service in Spanish. However, there are subtle differences in their usage and contexts.
Correo
'Correo' generally refers to the mail system itself or to an individual piece of mail.
Voy a enviar esta carta por correo.
(I'm going to send this letter by mail.)
El correo llegó tarde hoy.
(The mail arrived late today.)
Nunca recibí tu correo.
(I never received your mail.)
Correspondencia
'Correspondencia' is a more formal term, often used to refer to substantial communication, such as a series of letters, or the collective representation of all the mail received.
Tengo una gran cantidad de correspondencia que responder.
(I have a great amount of correspondence to respond to.)
La correspondencia se ha acumulado durante mis vacaciones.
(The correspondence has piled up during my vacation.)
"Historia de una correspondencia" es un libro sobre cartas de amor perdidas encontradas por el narrador.
('History of a correspondence' is a book about lost love letters found by the narrator.)
Summary
'Correo' and 'correspondencia' both refer to the concept of mail in Spanish, but 'correo' tends to refer to the system or individual pieces of mail, while 'correspondencia' typically refers to a larger volume of communication or the collective representation of all the mail received.