it is possible people do bad things
Take the necessary precautions like hardening the box, regularly auditing it, chrooting users and NOT allowing users to write data.
i was wondering i could have something more than just an ip and anyway i have got still nothing in my hands because is all spoofable stuff but sometimes can give you an idea if something weerd happens.
Take the precautions...
The greet mail is just an another idea to test mail validity that once reached destination allow anonymous login,just a security layer more ... still wondering !!!
There's nothing security-enhancing in providing a valid email address.