- Standard business envelopes
- Commonly used for invoices / bills
- Can fit in larger envelopes to be returned to the company
- Can be private or public
As the name indicates these are the standard size business envelopes where the number 9 indicates the length. Also known as Windsor these have the dimensions 3⅞ × 8⅞ (inches). This is an acceptable size by the North American postal service which will go through the sorting machines. There is still space in them after an A4 size folded thrice is slipped in them.
Mostly used for sending bills/invoices or other information to customers. Banks can use these #9 envelopes to send credit card receipts, telephone and electric companies for bills etc. They can also be used to return payment or reply envelopes as they can easily fit inside No. 10 envelopes - this being their biggest advantage.
No 9 envelopes could be confidential or not – confidential ones are those with plain envelopes and seals for pasting the flaps. The not so private ones will have die cut windows on them and normally pasted. Windows will let the recipient see the subject of the envelope easily.