The move comes three weeks after OptusNet suffered the same fate and was forced to ask BigPond's crack spam experts for assistance. Fellow ISPs TPG and iiNet also appeared to have made BigPond's blacklist of spammers for a short period at that time.
"Our mail servers were temporarily blocked by the BigPond mail servers at the start of this week," admitted a Westnet staffer in an e-mail sent to customers. "During this block any mail [from a Westnet customer] destined for a BigPond address would have been unusually delayed for a long period of time."
The staffer further admitted one of his company's mail servers "was used to send a large amount of spam".
A BigPond spokesperson claimed the situation was "good news" for his company's customers as it had successfully protected them from "what sounds like a serious spam problem".
"By the way, if they were blacklisted for spamming we would not be the only ISP to have blocked them," he added.
While details on the TPG and iiNet sister cases several weeks ago were not as conclusive, they would appear to mirror Westnet's trials.
Commenting on a sample blocked e-mail forwarded to ZDNet Australia by an iiNet customer, iiNet managing director Michael Malone said "it looks like it is being blocked at BigPond's end.
"So it's being correctly delivered to BigPond, but they are rejecting it," he said. "Sounds similar to the situation with Optus."
The iiNet e-mail contained the same error message as one published by a TPG user on the ISP's forum at popular broadband information Web site Whirlpool, but TPG declined to comment.
However, a BigPond spokesperson said at the time the company could not find iiNet and TPG on its list of spammers.
"That's not to say that some have not been blocked in the recent past and then taken off the list once the relevant spam issue has been resolved," he said.