Spamhaus provides lists of known spammers to businesses, enabling them to block junk mail in their incoming email traffic. It was taken to Court by e360 Insight, an email marketing company, which Spamhaus had added to its spam blacklist.
e360 told an Illinois court earlier this month that the spamhaus.org domain should be suspended, after it won a claim for damages against Spamhaus.
But in the Illinois Court last Thursday, the judge rejected e360's request for suspension.
Judge Charles Kocoras said that the relief e360 sought was "too broad to be warranted in this case", and that unproportional effects could be caused by suspending Spamhaus' service.
In a Court statement, Kocoras said, "The suspension would cut off all lawful online activities of Spamhaus via its existing domain name, not just those that are in contravention of this Court's order."
"While we will not condone or tolerate noncompliance with a valid order of this court, neither will we impose a sanction that does not correspond to the gravity of the offending conduct," the judge continued.
Some businesses had been concerned that if the Spamhaus service was suspended, the quantity of spam on the internet could have increased dramatically. Spamhaus claims it is responsible for stopping 50 billion spam messages a day.
Spamhaus is also disputing the $11.7m (£6.25m) damages that the Illinois Court has ordered it to pay, saying that the Court has no jurisdiction over a UK-based company.
After the award, e360 chief David Linhardt branded Spamhaus as "a fanatical, vigilante organisation that operates in the United States with blatant disregard for US law".
Internet registrar ICANN said earlier this month that it would not suspend the Spamhaus domain