I don't see how Arvixe could help in this case unless you want to change from using Yahoo email and use something that Arvixe provides.
It is a weird problem as I can verify you receive email at your domain if I mail you from my gmail but mail sent from our email server to your domain is bouncing back as user unknown. Whatever is causing that is probably also preventing the mail sent from your site, though other factors could also be involved in that case since your same address is likely the from address when mail is sent from your site.
Wish I had more advice for you but I know I never had good luck myself using Yahoo business email for my sites, newsletters sent from their servers were very often flagged as spam by receiving mail servers.