Is it normal for my Paypal IPN script to get hit twice every time?

[lizardboy]

I am currently testing an IPN script in PHP, using Paypal's sandbox.It seems to work fine, except that it seems to get hit twice every time. I put in some code right at the top to just send me an email alert so I know the script has been executed. I get that alert twice with every transaction.I can even comment out everything in my script except that line, and I still get it twice, so I think I can be reasonably certain the problem is not in my IPN script but something on the Paypal end.I don't know if this means I've got some setting in my account on Paypal wrong, or if there's a normal part of Paypal workings that I'm not understanding or what's going on. I'm pretty sure my IPN script shouldn't be running twice for every transaction, though.Is there a reason my IPN script would get hit twice? Is there something I can or should be doing about that?