We are seeing delayed outbound email to Microsoft (outlook, hotmail, etc). This appears to be a problem with their systems, though they are reporting it as this: "The mail server has been temporarily rate limited due to IP reputation." That said, no one works as hard as we do to combat outbound spam, and their complaint rates are very low. Our position, until we hear otherwise from them, is that this is an error in their system.
Postmortem
On Monday, Microsoft deployed a change to their anti-spam system. Soon after, mail servers all around the internet began seeing extremely high rates of defers from Microsoft. Some emails were accepted, some were deferred well beyond what many of us retry for. This wasn't just small senders that were impacted. Major corporations reported the same behavior, though not all of them did it publicly (and that's why I won't name them). If you were able to talk to Microsoft sender support during this time, they were entirely unprepared for this and all responses whether automated or human were not relevant or helpful. A fix was deployed Wednesday that resolved this. Everything has been clear since then.
Resolved Feb 26, 2026 at 2:50 AM UTC
It's over!
Investigating Feb 25, 2026 at 5:09 PM UTC
Day 3 of Microsoft being anti-competitive and trying to harm other ESPs. We've continued to receive reports from other email providers that they are seeing the same. We're working on multiple strategies to address this as best we can. Microsoft continues to pushback and swear that it isn't happening even when we send them thousands of lines of log entries. We WILL get this taken care of.
Investigating Feb 24, 2026 at 5:05 PM UTC
We have some solid numbers for the last 17 hours: 46549 emails successfully delivered to Microsoft. 3256 emails passed to our backup relay because MS endlessly deferred them. So while they are accepting the vast majority of your emails, we're handing over a small portion to mail.baby (the backup relay we use) to try a few more times before giving up. This appears to be something that all mail providers are dealing with today, whether or not they're talking about it.
Investigating Feb 24, 2026 at 4:57 PM UTC
It's getting worse today. This should be treated as a major outage for Hotmail, Outlook, and Live users. Office 365 users are not as impacted. We're trying to work with Microsoft, but it's been almost 24 hours now and they seem unaware of the outage.
Investigating Feb 24, 2026 at 4:29 AM UTC
Honestly, no one likely notices the delays at this point. Volume is down at this hour, we're sitting on an average of 50 emails queued waiting for Microsoft to accept them. It's not a big deal, but it is still a thing.
Investigating Feb 24, 2026 at 12:28 AM UTC
Still happening to various mail providers, though most of them probably don’t notice. It’s not a gigantic issue, it’s an average of 100 emails sitting in queue at all times while they slowly allow mail in. Given the small scale, it’s unlikely anyone who can fix this at MS is even aware of it. We’ve reached out, they’ll probably reply that everything is fine 2 weeks after they fix it.
Investigating Feb 23, 2026 at 9:40 PM UTC
Second report came in, this is definitely not just us.
Investigating Feb 23, 2026 at 9:18 PM UTC
We've received 1 response indicating that we are not the only ones who started seeing this today.
Investigating Feb 23, 2026 at 8:52 PM UTC
We are seeing delayed outbound email to Microsoft (outlook, hotmail, etc). This appears to be a problem with their systems, though they are reporting it as this: "The mail server has been temporarily rate limited due to IP reputation." That said, no one works as hard as we do to combat outbound spam, and their complaint rates are very low. Our position, until we hear otherwise from them, is that this is an error in their system.