Buy mail then attach it to your Pokemon write whatever then trade that Pokemon to a friend they can read it then send it to there PC.
Chat with our AI personalities
to send air mail(or any other type of mail in any game) you have to give the mail to a Pokemon and trade the Pokemon to somebody else so they get to read it.
There is no best Pokemon on Pokemon HeartGold.
there is no Pokemon Mansion in Heartgold.
You can write letters to your friends. Just put a message on the mail. Give the mail to one of your pokemon, and trade with a friend.
They are not in Pokemon HeartGold