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Admins accuse Microsoft of Draconian Hotmail cap

'Only 10 recipients at a time, please'

Internet Security Threat Report 2014

Life can be tough when you're one of the globe's biggest email providers. Just ask Hotmail. Users get upset enough when come-ons for Viagra slip through the cracks of the Microsoft-owned service. But there's just as much hell to pay when its war on spam snuffs out legitimate emails.

In May, we reported on a proprietary Microsoft technology dubbed SmartScreen, which secretly blocked Hotmail-destined email from entire domains - even when they were a year or more old and were correctly listed in the DNS and had solid SPF records.

Now we're fielding reader tips that Hotmail has placed Draconian limits on the number of Hotmail recipients who can receive an email. The first 10 Hotmail addresses included in a mass email go through just fine, according to these reports. But any additional addresses are returned to sender with a message that reads: "552 Too many recipients." (Microsoft denies it has placed any such restriction on the number of senders.)

That's causing considerable trouble for people like William Old, a UK-based IT administrator who maintains an email newsletter for retired police officers. After sending the most recent newsletter about two weeks ago, he quickly received the 552 notice informing him that 29 of the 39 Hotmail addressees were being returned.

"The issue for us is it's a blow to a well established mechanism for getting an update out to our 550 members," Old says. "It was working perfectly well up until the last month."

Old has since sent several batches of test emails, and each time, exactly 10 are delivered to addresses ending in hotmail.com or msn.com and the rest are rejected with the same 552 failure notice.

It took Microsoft's rapid response team more than 19 hours to provide a three-sentence response to our request for comment. It read:

Microsoft is committed to helping protect email as an essential communications tool and to help protect users worldwide from spam and other e-mail safety concerns. One of the methods we employ to prevent spammers from abusing Windows Live Hotmail is to establish a sending limitation of 250 recipients per day. We do not currently limit the number of recipients per message, however we may consider doing so in the future for new accounts, as additional means to prevent spammers from abusing Microsoft services.

Microsoft's denial doesn't square with recent online discussions in which users report a new spate of 552 failure notices being sent by Hotmail. The initiator of this discussion, for instance, reported that six of 16 messages sent to Hotmail users bounced and said the rejection was a new phenomenon. Other discussions like the one here also appear to report the same cock up.

Microsoft denied our request for an interview with a Hotmail official.

Several people have reported a work-around, which can be achieved by setting the max_rcpt of the SMTP transport to 10 or less. This method worked for Old, but he said it has the potential to consume significantly more bandwidth, a limitation that is sure to hurt legitimate senders but have much less of an effect on spammers, who don't pay for their internet service.

The last time we spoke with a Hotmail official, we learned that of the 5 billion emails sent to its users each day, about 4.5 billion of them, or a whopping 90 percent, were spam. Clearly, unsolicited email is a problem that warrants a tough response from Microsoft.

But the sudden reports of 552 rejection notices are a reminder that brute-force solutions are just as likely to trip up legitimate senders as they are in shielding their users from spam. In this case, it would also appear to violate RFC 2821, which states: "Rejection of messages (for excessive recipients) with fewer than 100 RCPT commands is a violation of this specification."

So the next time you send email to a Hotmail user, give a moment of silence for the beleaguered security pros at Microsoft whose collective finger are all that's blocking a torrent of spam and other crud from spilling over the proverbial dike.

Then say a little prayer that the people you're trying to reach actually get your message. ®

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