The best part about this software is its ability to validate emails in bulk which saves time from manually checking each one of them individually. I dislike how it's not possible to use other domain names or sub domains when using zero bounce with my ISP account (like Google Apps). It works great but sometimes if there are too many people trying to register at once their servers get overwhelmed and they stop working temporarily. This happens almost every day during peak hours like morning rush hour times where we have thousands of new registrations per minute. We used to receive tons of bounced messages due to our users registering multiple accounts under different aliases. With Zerbouncer all those bounced mails were converted into undeliverable ones automatically saving us time by filtering out these unwanted records. Nowadays no more bouncing!