So, the Sherlock in me will begin sleuthing:
Clue #1: Postmark.
Visible word "REGION MC" across the stamp. Black envelope makes it hard to see, but ink is shiny. If I hold envelope just so I can make out the word "HUNTER", so altogether it says, "HUNTER REGION MC".
Conclusion: RSVP is from NSW, this means that it is a member from Zac's family or it's Kym Rolle, probably not Stephan and Carla because they live in Sydney, probably not Di, because she lives a little more north than the Hunter, although it is entirely possible her mail went through HUNTER REGION MC.
Possible RSVPers: Clare family, Scarfe family, John and Pat Gageler, Alan and Donna Gageler, Di Gageler, Kym Rolle.
Clue #2: Ink stamp.
I can make out a square border in the centre of the envelope at the top. So I hold the envelope under a halogen lamp, yields great results. I see a rectangle border with "30 MAY 2010" written within... I also see the letters "AMP" further along, which I can only assume is the end of "STAMPS". Why does it say stamps? Is this a vital piece of the mystery that I am missing. I MUST FIND OUT. Closer inspection reveals a jumble of letters, the ink is already starting to degrade... "AL" "ISE". OH MY GOSH. IS THIS A SUBURB OR SOMETHING? No, it just says "PERSONALISED STAMPS NOW AVAILABLE". Darn advertising.
Conclusion: This RSVP was sent 30th May. Not much to go on, really.
Clue #3: The way the dot was done.
Ball point mark was meant to be a dot, they didn't tick. This must have some psychological meaning but I have no idea what it could be... Sherlock would probably say it's because they are a neat person - a girl perhaps, or a boy who can do away with unnecessary flourish. The dot has been gone over a few times, possibly to make the ink darker. Ball point pens don't work so well on the soft cotton paper. The frustration is evident, I can see they've gone over the same spot 2 or 3 times. This must surely have a psychological meaning, but I don't know what it could be...
Conclusion: Not much really.
Clue #4: Writing on RSVP card.
Black ball point pen used, no name, no number of guests. God forbid they have an allergy to peanuts because we'll never know their dietary requirements! And, they are attending our wedding. Yay! If only we knew who they are and how many there are.
Conclusion: Kym Rolle did not send this RSVP. She is arty and creative, she would have whipped out all sorts of pens and because she is creative and knows it, she would have written her name all over that junk. The Clare family's RSVP would have been written by Michelle, who will at least have written the amount of people coming along (which we know to be 4). The Scarfe's family response would have been so thorough that they also would have written how many were attending, they are very thorough people. I'm betting John and Pat Gageler would have written their names and dietary requirements and that they are both attending.
Possible RSVPers: Alan and Donna Gageler, Di Gageler.
This RSVP was most probably sent by Alan Gageler (which would explain the frustration of grinding the ball point pen over the same spot and missing the other things to fill out. Perhaps he was frustrated because he had already filled out an online RSVP before he got the invitation and didn't want to do it again?
OR, it's Aunty Di, who was so excited by getting the invitation (as she has mentioned on facebook) that she grabbed the nearest pen, realised it didn't work and in her haste and excitement forgot to write whether she is allergic to peanuts or not.