I have downloaded MailDrop from the company page but when I try to install it on my Mac the error message appears "Maildrop can't be opened because it is from an unidentified developer".   My security is set to allow installation of only apps from the Mac App Store and identified developers, and I don't particularly want to change this (even if I knew how). What should I do? 

I have downloaded MailDrop from the company page but when I try to install it on my Mac the error message appears "Maildrop can't be opened because it is from an unidentified developer".   My security is set to allow installation of only apps from the Mac App Store and identified developers, and I don't particularly want to change this (even if I knew how). What should I do?