I want to improve our mail server lists by handling all the bounces we get in our websites. I have a website which has over 8000+ users and another website which as over 1500+ users, they are emailed various notifications every second, ie. job alerts, email alerts,

I am using POP connections with EXIM on APACHE server, most scripts are based on PHP language generates email on the fly.

Problems i have

1. But some users has registered long time ago and now quite few has bounce email address
2. Some users register with dummy emails like [email protected] which never existed but a valid email address, any chance of stopping this without asking them login to the email account and clicking links which dont work most times.. (too annoying to the end user)
3. Server is sending unnecessary emails can be avoided if i know they dont exists ?

Solutions i need to have

1. Is there a way i can download the bounce email list somewhere (WHM/Cpanel), i know exim mail has it but its not readable (i need a file like CSV or something similar to scan them over and write a php script to delete the users from the database ?)

2. I need to know if there is any function in the PHP that can check the existence of the email address on the fly ? so that i can set the email send function in the mailer class to check before it sends out.

3. On the server will bouncing emails are going to eatup lots of server resources ? like memory/cpu on processing them ? or are they are minimal where we dont have to worry about this at all ?

4. May be a opensoruce or linux software to capture them and view them in a report basis and cleaning them up ?

I am not a linux expert or server admin but i do lot of PHP coding, so please be descriptive of the solutions specially if they are linux commands

Thank you!