The Customer want to use SMTP port 25 without SSL to send the email , but Exchange 2007 default setting need the client use SSL for smtp ,somebody suggest modify the Receive connector Permission Groups,allow the Anonymouse users,but doing this ,anyone can use anyother accout to send other email!Its very unsafty! Anyone can help me ?

The allow annonymous just allows access to relay into your domain, not open relay. 07 is opportunistic TLS by default, so it only encrypts when it can, not by default. http://technet.microsoft.com/en-us/library/bb430753.aspx