Letters: Elements of a letter design

Address block

The address block is the portion of space on the top of a letter's first page that's visible through the envelope. It includes the sender and recipient info.

Envelope window

All letters are mailed in an envelope. The envelope has two windows that show elements of the address block. The top window even offers a bit of extra space above the address block so you can add your company's logo. 
Fold lines

The fold lines indicate where your letters will be folded over. 

Tracking

Internal tracking codes are added to each letter.