PostcardBulkMailing.com

If mailing your marketing postcards through the United States Postal Service USPS you want to first make sure that you are creating your postcards within the official size and shape to be classifies as a postcard. 

A postcard must be:

• Rectangular
• At least 3-1/2 inches high x 5 inches long x 0.007 inch thick
• No more than 4-1/4 inches high x 6 inches long x 0.016 inches thick
  
  

The number of postcards you mail, the zip codes they are mailed to and how you sort the postcards before mailing will have a huge impact on the cost of postage per 4x6 postcard.

You can calculate the postage cost of 4x6 postcards online at USPS official website http://dbcalc.usps.gov/CalculatorSetPage.aspx.

The price category will be higher or lower depending on the following:

5 digit  and number of postcards mailed

3 digit and number of 4x6 postcards mailed

 AADC and number of postcards mailed

Mixed AADC and number of postcards

Those prices range from 0.205 to 0.230.  You can also calculate the price for presorted postcards and single- piece postcards, automation postcards and machinable postcards.  All of the postcard mailing categories have special discount pricing available and can be calculated online.

http://pe.usps.com/text/qsg300/Q230c.htm Page on USPS website that contains listing of bulk mailing prices