postcard with a reply card attached

(formal) friend

reply, response

to reply, to respond

a round trip, going back and forth / (by extension) an exchange (of conversations, letters, etc.) / coming and going

a round trip, going back and forth / coming and going / (by extension) exchange (conversations, letters, etc.)

postcard

to use / to employ / to make use of, to apply / to spend

imperfective and stem (or continuative) forms of 送る (okuru) [ichidan]

To send