The ease of use, how straightforward it was to set up our SMTP servers as well as receiving notifications when they were updated/downgraded. I have not found any downside yet! If my experience continues like this then we will be able to fully rely upon them from now onwards too without fear or doubt at all!! There really isn't anything bad about their services other than perhaps if you're looking into something more complex there may take slightly longer than expected time before things get configured correctly etc., but nothing massive either way :) Just keep using coreSenders until everything's perfect ;) A fantastic product with excellent support behind them which helped us make some great decisions regarding mail forwarding between two different providers (Comservices). Easy to configure, simple interface with many tools available. In this case of emails it is fast without any delay or failover system. This tool support all known major platform like Microsoft Word/Exlorer, Gmail, yahoo etc., It provides easy way to send Bulk Emails at different platforms as well as we could track each mail individually according to its tracking link. We could use bulk sending option to send out our monthly report by giving specific date range for various departmental mailing.