As I’ve been thinking about the different things that I want to check on each email message I keep noticing that most important technology for checking information is DNS. RBLs, SPF and even checking to make sure that the domain name that is sending the email has a MX record or that it even exists all relies on DNS.
Being that the first four or five things that I want to check on each email message relate directly to DNS that means that the DNS server will need to perform well and cache information and the DNS Client that is doing the DNS Queries will also need to perform well.
So I am currently looking into DNS technologies to see which one I am most interested in using.