Anonymous

My friend who is on vacation send me a postcard.

Anonymous

I got a postcard from a friend. He is vacationing in Miami, Florida. I received a postcard from a friend. He is vacationing in Miami, Florida. My friend is vacationing in Miami, Florida. I received a postcard from him today.

Anonymous

My friend, vacationing in Machu Pichu, sent me a postcard which I received today.

Anonymous

I (received/got) a postcard from a friend who is on vacation.

Anonymous

I got a postcard from a friend who was on vacation.

Anonymous

If you mean you 'received' it: I got a postcard from a friend on vacation. Adding the location would make sense.