Dirk Eddelbuettel | 15 Mar 16:56 2013

Your BTS does not cooperate with Comcast

I use Comcast which happens to be the US's largest ISP.  I have to use them for
SMTP delivery (as they block the outgoing port).

But sending mail from me to you BTS fails for your greylisting, and Comcast 
being Comcast goes into _abort_ rather than _retry_.