[exim] error 451-Could not complete sender verify callout ?…

Hi
I'm trying to subscribe to a list from a valid that I use every day what have I done wrong ? or mis configured in my attempt to block spam ..

Error as follows :

"

The address to which the message has not yet been delivered is:

  openvpn-announce-request@???
    Delay reason: SMTP error from remote mail server after RCPT TO:<openvpn-announce-request@???>:
    host mail.sourceforge.net [66.35.250.206]: 451-Could not complete sender verify callout
    451-Could not complete sender verify callout for <greg@???>.
    451-The mail server(s) for the domain may be temporarily unreachable, or
    451-they may be permanently unreachable from this server. In the latter case,
    451-you need to change the address or create an MX record for its domain
    451-if it is supposed to be generally accessible from the Internet.
    451 Talk to your mail administrator for details.
"

--
Gregory Machin
CT-Net
www.ct-net.org
greg@???
phone : +27 12 379 3497
fax : +27 12 379 4113
Cell : +27 72 524 8096

humans do not use the address
below its for trapping spam.
spamtrap -imasucker@???