my emails are bouncing back please help

I desparately need a MSN technicial to help me sort this out because it is affecting my business. Clients are sending me emails to my Hotmail acct and they are bouncing back. I am not seeing them. Also I am not seeing my sent emails so I am wasting time having to resend everything from gmail. Please help urgently or I will have to shut this email down and go elsewhere for better service.