Reply Mail appears in 7 version groups since Generation V, an All mail item in the Mail pocket
PokéAPI item 574 of 2,223, All mail category, Mail pocket
Effect, in PokéAPI's words
Reply Mail: “Lets a Trainer write a message and send it via Pokémon trade.”
Reply Mail shares its longer effect text with 35 other All mail items; it is quoted once on the category page. All mail
Games
Reply Mail is listed in the text of 7 version groups, first in Generation V
Game index by generation
IIIIIIIVVVIVIIVIIIIX
Named in
Black and WhiteBlack 2 and White 2X and YSun and MoonUltra Sun and Ultra MoonLet's Go Pikachu and Let's Go EeveeSword and Shield