Drop somebody a line/note - Idioms by The Free Dictionary
drop somebody a line/note
drop a line
Correspond, write a short letter or note. For example, I hope you'll drop me a line soon. This idiom uses line in the sense of "a few words in writing," a usage first recorded in 1647.
drop somebody a ˈline/ˈnote (informal) write a short letter, message, etc. to somebody: I dropped her a line inviting her to my birthday party.