best logic to show coupon only once?

Placebo

Need logic behind this.
say Im sending a newsletter and it has a link, 'click here for coupon'

on click [custom link with users email in url, so i use GET to flag them]basically a custom coupon is generated, but i need this to only be displayed once. Obviously easy php/mysql, where after page is loaded i flag that user so next time they go to the page nothing is there.

its sent via email so there are no logins etc, i only have their email, so its sent via email.

it one coup per person so problem is some people may click it and not print it and when they go back, it wont be there.

so only solutions i can think of is
Email them the coupon as a pdf? [any links for php-> pdf]
use cookies and allow a day ?

any other ideas?

thanks

forbairt

Why shouldn't they be able to print it a few times ?

They see the coupon they print it 50 times
They don't print it they go back and they can't print it
Your logic is slightly flawed to begin with no ? (if you're trying to stop them printing multiple coupons)

Can you lock it down to a serial tied into their email address or something ?

for your PDF option .. http://www.fpdf.org/ is quite shiny (or at least it was about 2 years ago when I was using it on stuff)

Placebo

well thats nothing i can stop for one, secondly coupons are obviously valid one per transaction. So its more likely some one will go back at a later date and then print it [as the coupons themselves are valid for a few months]

we have barcodes but problem is barcodes will scan none the less. So they will get away with it

Pixelcraft

but that's the only way you can limit the uses, on scanning the barcodes. You can't stop a user printing out something on their pc, even if you make it difficult, you can't stop it.