US Post Parameters
In the US, we print on US Letter size paper (8.5in x 11in). You will still need to upload your letter in A4 size, we will automatically resize it for you. You can refer to our letter template guide here.
We use double-window envelopes which are 9.5in x 4.125in in size.
The single address line formatting is the USPS formatting choice, see their example here. We will re-format any 2 line address for you automatically.