Hostgator is telling me they are using port 25 - out port. Is there something in your code that directs HG servers to use port 25? I want them to use port 3535 but they tell me that's not an email port. The reason I say this is because I was having so much trouble with Outlook sending my mail earlier this year. When I called GoDaddy about it, they said it's a Microsoft problem and port 25 was overwhelmed. They suggested I use port 3535 as my out port and it's worked great ever since. I've also had clients make the same change and they've had no more problems.
I also tried the contact form on classic pumps and it worked just fine with email@example.com so I changed the order form back (had been using a yahoo address) and tested it and it worked fine. That tells me that sometimes the email goes through and sometimes it does not. It has nothing to do with the code (as you have stated).
I believe it's the same issue I was experiencing with my email through Outlook so if there is some way I could change my code so my forms would use port 3535, I think the problem would be solved. I'm not sure obviously but it's my best guess right now.
I still don't understand what port 80 does and I'm not sure I'm even using the correct port there. Please tell me if I should change that.
Thank you again. I really appreciate your expertise in getting to the bottom of this.