Letter Question

[Unregistered333]

I would like to write a letter to a person who works with other people in a department.
So my question is, how can I address that letter exactly to a known person from that department?
For example:

"ADDRESS....
............
ON HANDS OF MR. ……"

Thank you.

[Tdol]

I'd put

Name
Depatment
Comapny
Address

On the envelope

And

Department
Company
Address

Dear Mr x,

in the letter.