I have a HP Officejet Pro 8600 Plus and can't print a 5.75" x 8.75" envelope. I don't understand why HP doesn't let you customize envelopes anyway because everybody has needs for different sizes. I can print a #10 envelope on Microsoft Word but can't on my Hallmark Deluxe Studio Card program. I put in #10 on my software and & put a #10 envelope in my printer but & get mis match error. I use to have HP Officejet 7310
& I had no problems with customizing any size envelope. If HP made printers that did, I can't understand
them not making printer to custom support different sizes now.