BT Openworld is hopeful that a spam blacklisting group will remove an email block on it by this weekend.
The Distributed Server Boycott List (DSBL) blacklisted the internet service provider (ISP) after claiming BT's servers could be exploited by spammers.
BT became aware of the problem around two weeks ago, when a number of its BT Connect customers were unable to send emails to users of ISPs that subscribe to the DSBL list. The emails were bounced back with delivery error messages.
The firm then wrote to the DSBL, but was told last Saturday that it would be another seven days before any action could be taken.
DSBL said in a statement on its website: "The person who runs the mail server at that address has chosen to refuse email from dangerously misconfigured, insecure, or abuseable servers based on a list that we publish.
"Blocking mail that originates from servers in our list can significantly reduce the amount of spam that users of their mail server receive."
This means that when somebody attempts to email a server that uses the DSBL blacklist in its anti-spam configuration, the emails are refused.
BT denies that its servers can be abused and said there was no evidence of spam to support the accusation. But it did admit to vnunet.com that it altered its server configurations last week.
Nick Truman, head of abuse at BT Openworld, slammed DSBL and said communication with the group had been hugely problematical.
"We have had no reports of spam and have tried to talk to DSBL on behalf of our customers but had no joy. Once you are on their list you are doomed. They are not properly organised and there is no way to enter into correspondence with them unless we email them.
"Even the ISPs that sign up for the list have no access to them. But we have made these minor modifications and notified BT Connect customers of the situation."
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