Customers of the MessageLabs spam filtering and e-mail security service have been unable to send to Windows Live accounts, such as Hotmail addresses, since Friday.
UPDATE (14:38): The ban does not appear to be affecting all MessageLabs customers as initially reported. Some customers who route their out-bound mail through US-based MessageLabs servers appear affected, but Risky.Biz has identified at least one customer, routing through Asia-Pacific ML servers, that is not affected. Looks like it's just some of the US-based MTAs that are blocked.
"We have been recently made aware that Windows Live has implemented a block on our IP address," reads an automatically generated email from MessageLabs in response to support requests. "We are in the midst of engaging their support teams to reach a resolution on this case."
Risky.Biz has confirmed the block is still in place after three days. The 4th of July weekend in the USA is no doubt hindering efforts to remedy the situation.
Automated 'bounce' messages from Windows Live Servers state the ban was imposed because MessageLabs email servers "exhibited namespace mining behaviour," which is commonly associated with spamming.
MessageLabs, which is owned by security software maker Symantec, is a popular service among enterprise customers. In Australia its client list includes insurer QBE, Westpac Bank, Colonial First State, 172 local governments in New South Wales, the NSW health department and airline Virgin Blue.
Many MessageLabs customers use the company's service to handle both inbound and outbound email messages for compliance reasons.
Spokespeople for both MessageLabs and Microsoft were unable to comment at the time of writing.
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FULL DISCLOSURE: Both Symantec, the owner of MessageLabs, and Microsoft are Risky Business sponsors.