You can use post to refer to letters and packages that are delivered to you.

A post in a company or organization is a job or official position in it, usually one that involves responsibility.

A post is a strong upright pole made of wood or metal that is dug into the ground.

On a horse-racing track, the post is a pole that marks the finishing point.

Post up means the same as post.

If you keep someone posted, you keep giving them the latest information about a situation that they are interested in.

If you post notices, signs, or other pieces of information somewhere, you attach them to a wall or board so that everyone can see them.

If you post information on the Internet, you make the information available to other people on the Internet.

If you post a letter or package, you send it to someone by putting it in a postbox or by taking it to a post office.

If you are posted somewhere, you are sent there by the organization that you work for and usually work there for several years.

If a soldier, guard, or other person is posted somewhere, they are told to stand there, in order to supervise an activity or guard a place.