The main envelope will fit one main card, one insert, a response card and a response envelope. This is also the maximum number of items allowed to be added per order. We don’t recommend trying to mail more than this in a single envelope, otherwise you may see an increase in the cost of postage to mail your cards.
An envelope containing a card, insert, response card and response envelope would normally be under an ounce, so a first class $0.47 stamp or forever stamp would be suitable for rectangular cards and envelopes.
For square cards and envelopes, extra postage is required. See here for more. We recommend taking a fully assembled envelope to your local post office to make sure you get the right stamps. You can also check the USPS website to calculate weight and postage.
Please note: The information above refers to rates within the United States. Rates in other countries should be verified with the local post office.