A mailbox with letters inside and a bird standing atop.

Mailbox With Letters And Standing Bird

A cardinal direction of an arrow pointing to a capital letter N, representing the North.

North Sign With Arrow

An envelope opening to show a piece of paper.

Lines representing text on a piece of paper in the style of a letter or assignment.

A "write a review" illustration with a long paper, an ink pen and a star icon. 

A speec bubble with three Z letters, indicating sleep.

Envelope attached to the string of a floating balloon.

An opened envelope with a letter coming from it.  

A curved outdoor mailbox with an envelope half sticking out of the mail slot. 

An open envelope with a pointing cursor and a letter with a notification icon on its top corner.

A busy and overworked manager or employee surrounded by charts, graphs, and notifications.