If you have an Outlook, Hotmail, Live, or MSN email address, don't assume every missing email ended up in your spam folder. A recent issue caused some messages sent to those types of email addresses to be rejected and bounced back to senders instead of reaching recipients.
It might seem like a nice break to not get emails for a few days, missing important messages can cause issues. The underlying cause was a mistake related to spam enforcement rules. Microsoft has rolled back the update that included the problem, so normal functionality should be restored.
"Some users may intermittently be unable to send email messages to Outlook.com, Hotmail.com, or Live.com email addresses," explained Microsoft in an incident report highlighted by the website lazyadmin.
While the issue was related to spam enforcement rules, affected messages did not simply end up in recipients' spam folders. Microsoft's mail servers rejected the emails and bounced them back to senders instead.
That's an important distinction because recipients have no way to find emails that were never delivered. If you were expecting an important message over the last few days and it never arrived, it may be worth following up with the sender rather than digging through your spam folder.
The issue may also have gone unnoticed in some cases. If someone claims they emailed you recently but nothing ever arrived in your inbox, there's a chance the message was affected by the bug and returned to the sender before reaching your account.
Senders may be able to determine if they were affected by checking for non-delivery reports, sometimes called bounce messages. Errors mentioning Outlook.com, Hotmail.com, Live.com, MSN.com, or codes such as "550 5.7.1" and "AS9031519" could indicate that a message was rejected during the incident.
A successful resend also does not necessarily mean there was never a problem. Reports from affected users suggested the issue was intermittent, with some messages bouncing initially before being delivered successfully when sent again later.
I occasionally need to check my spam filter to find messages that were mistakenly flagged as spam. This happens more when work emails are involved, but Outlook can be overly aggressive with personal emails as well.
But this bug was different. Instead of being delivered to a spam folder, some messages never reached recipients at all.
The issue was primarily related to mail destined for consumer Microsoft email accounts, including Outlook.com, Hotmail, Live, and MSN addresses. Microsoft 365 business mailboxes were not the focus of the reported delivery failures.
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