Why sit and wait for an email, their number is on their website, under parts and service. 800 363 3555
I have the same problem, I just bought a used 500 in rough shape (dinged up, rusty) and I'm refinishing it myself. Everything seemed to be fine but after I had the receiver in the parts washer the safety is very hard to move.
I've called twice in the last week and their customer service has been top notch. I was missing the screws for the tapped receiver and called to get the size. I was on hold maybe one minute when they answered they asked for the serial number and got my information and sent me new ones for free, I didn't even ask.
I called this morning about the safety and didn't have to wait at all, answered on about the second ring. I was told all work on the safety would be free of charge you just have to send it in to them, or take it to a gunsmith and they would cover it. I'm assuming it would have to be one of their approved dealers or something. I thought I could fix it myself which he didn't recommend but told me to try and put some lube on it if all the parts were in correctly.
Don't lose faith in Mossberg just yet, I own two other 500's and have never had a problem at all out of either of them, and from what I've experienced in the last few days their customer service is pretty good.