Today while I was busy trying to debug an email issue trying to send email to a facebook group that keep on bouncing the email based on authentication failure I came across this website. http://isnotspam.com/ Facebook is full of nonsense to try and filter out spam. Obviously most of us running servers do exactly the same to some extend. isnotspam will check your email for the following; SPF Check Sender-ID Check DomainKeys Check DKIM Check SpamAssassin Check My issue was (hopefully) the fact that DKIM was not set up on the server hosting the remote DNS. Don't you just hate it when a client / his representative adds "A records" instead of updating the NS for the domain?