[exim] retry question

Hi,

I am having a very difficult time sending email to att.net with the
default Exim 4.62 configuration. Att.net gives me 450 Busy Retry error
on almost all email I send to them right after the connection attempt. I
notice that if I manually resend using exim -M <emailid> many times,
like once every second for 30 seconds, the email usually goes. What
configuration should I try in the configure file to make this happen? I
tried this but it doesn't work.

att.net rcpt_450 F,1m,1s

Is the hints database preventing the retry? Please let me know how you
send to att.net or how I can make this work.

Thanks.
Craig