Right, people want to blame it on Microsoft, but who designed the form? Who set the criteria for mail delivery? There are millions of other web sites in the world with forms and none of them have this problem with accepting email from one of the world's largest email providers.
Wait, wait... people shouldn't post "opinions" about overstay if they don't have the facts. Last time I checked it was 500 baht per day up to a maximum of 20,000 baht. Has that changed? Overstay less than 90 Days = 500 Thai baht/day overstay fine (maximum 20,000 Thai baht)
Overstay more than 90 Days = 1 year ban from Thailand and 20,000 Thai baht overstay fine
Overstay more than 1 Year = 3 years ban from Thailand and 20,000 Thai baht overstay fine
Overstay more than 3 Years = 5 years ban from Thailand and 20,000 baht overstay fine
Overstay more than 5 Years = 10 years ban from Thailand and 20,000 baht overstay fine