I have a problem at the email setup in magento.
When I using firstname.lastname@example.org in all sales order email, my client with email@example.com or other email have not problem after click the checkout button at the last page which will direct you to a page that comes with order no.
But when I using xxx@<personal>.com in all my sales order email, my client with xxx@<personal>.com <-- same as my domain will be able to confirm and direct to the order page whereas other email like gmail, hotmail or hotmail will have error and it not direct to the order no. page. But the order still goes into my admin page.
Do anyone know how to solve this problem? either by editing the code or something to do with my email system?