Hi Alan, this occures from time to time unfortunately.
You might like to take a look at the following CS news item about the problem and how to get around it. You'll normally need to check with the spamhouse link to see if your email address has been blacklisted and follow their guide to get it off a blacklist: https://crowdsupport.telstra.com.au/t5/Telstra-and-or-BigPond-Email-KB/Why-is-my-email-being-blacklisted/ta-p/76234
