When sending mail to outside a few additions would be quite necessary: 1. Insert inside header a X-remark like: This mail is sent from a webhosting server. If you receive any spam or unwanted mail please contact <adminmail> first before reporting to public SPAM lists. This can be done by using an SMTP proxy for outgoing mail which is able to add some information to the header. 2. Insert inside header a X-remark like: X-Script: This mail is sent from script located at <path> This is helpful when user uses a buggy script to easily detect where the script is located. 3. Block outgoing massmailing and bcc by default. Block outgoing mail by default to x mails / hour and/or max. x receivers (bcc/cc) per mail. This prevents the system from beeing used as spamrelay if a script is insecure. It happens quite often that webhosting customers uses insecure scripts and if you are not able to block these server will be listed on RBL very fast. This is to prevent your server from beeing listed as spam relay on RBL - because it's very hard to remove a listed server from the lists and when it's listed many other receivers can't receive mails sent by your listed server.