authenticate email script

My existing web site used to 'autosend' registration e-mails to users and CC to admin when they registered, and admin would also get CC's of any orders placed. I am told by the server host that they increased security by changing the software, now these 'auto' emails no longer get sent. The server host said we need to activate authentication in the script "Keith C: bascially you need to create a valid email account with a password, and setup your script to send using that account + password, thus authenticating the email " I looked this up on the internet, and it is beginning to look very complicated. I need someone to sort this out for me please.