I like how easy it was, in about 10 minutes we were up & running! It's very well documented so there wasn't much learning curve at all (very pleased!). We're using this as part of our email platform across multiple clients - no problems here either way! The only thing i'd say could be improved would perhaps have more options when setting your hostname/domain? There are some limitations but nothing major or anything too bad really. Just need to know what settings work best depending upon which client systems they will run from etc. Have been able to use their API integration tool within my code without any issues since day 1! The most important thing about this software, it's easy of use! I have no problems at all using SPMTPD in my own systems (both Windows Server 2008 R2 & Linux). It has been very useful as well since our customers are also able send email from their computers without having any technical knowledge or experience needed by them when they want sending mail throught webmail services like Gmail etc..