Keeping the Inbox Safe: Microsoft’s New Bulk Email Rules Explained

Microsoft has finally joined the bulk sender requirement club! After the announcement and implementation of Gmail and Yahoo’s bulk sender requirements, email experts speculated it was only a matter of time before Microsoft followed suit and released their own. But what does this mean for email marketers?  

Microsoft’s announcement

Effective May 5, 2025, Microsoft began enforcing their recently announced bulk sender requirements. Let’s identify and define them:  

Bulk Senders are defined as sending 5,000 or more messages a day to Microsoft domains, most notably outlook.com, hotmail.com, and msn.com. Senders meeting this criteria must now comply with Microsoft’s requirements which are outlined below and are detailed in their official announcement: 

SPF (Sender Policy Framework) 

• Must Pass for the sending domain. 
• Your domain’s DNS record should accurately list authorized IP addresses/hosts. 

DKIM (DomainKeys Identified Mail) 

• Must Pass to validate email integrity and authenticity. 

DMARC (Domain-based Message Authentication, Reporting, and Conformance) 

• At least p=none and align with either SPF or DKIM (preferably both). 

Established senders should already have these authentication protocols in place, as they became mandatory for both Yahoo and Gmail in 2024. However, our DMARC adoption study results from January 2025 might surprise you. It revealed that a staggering 84 percent of domains and subdomains used in email “From” addresses do not have a published DMARC record. Furthermore, out of the small percentage that do, 7.64 percent possess invalid records. 

Microsoft’s bulk sender requirements have changed since the initial announcement in April. They originally intended to place non-compliant mail into the spam folder; however, their amended statement says they will now immediately reject mail that fails any of the above checks. Be on the lookout for a new bounce code and reason. If you aren’t compliant, you’ll receive this: “550; 5.7.515 Access denied, sending domain [SenderDomain] does meet the required authentication level.”
 

What could be around the corner 

In their announcement, Microsoft teased what I suspect will soon become requirements. For now, though, they’re only strongly recommending the following additional items: 

• Compliant P2 (primary) sender addresses: Ensure the “From” or “Reply‐To” address is valid, reflects the true sending domain, and can receive replies.  

• Functional unsubscribe links: Provide an easy, clearly visible way for recipients to opt out of further messages, particularly for marketing or bulk mail.  

• List hygiene & bounce management: Remove invalid addresses regularly to reduce spam complaints, bounces, and wasted messages.  

• Transparent mailing practices: Use accurate subject lines, avoid deceptive headers, and ensure your recipients have consented to receive your messages.  

Let’s discuss these individually. The one that has most senders feeling a bit anxious is the first bullet around replies. Technically you can still use “no-reply@” provided a reply is supported by a valid domain that is fully authenticated (A record, PTR, the whole nine yards). However, from a subscriber perspective, it could be perceived as though someone you wanted to chat with has their palm up in front of them to stop you (which isn’t very nice).  

Are auto-responders compliant? Yes, they are, since the mailbox accepts and auto responds to the subscriber, guiding them on how to reach your customer service teams. Take, for instance, how Hickory Farms manages replies to their marketing efforts. You might consider including your team’s phone number. However, remember that those replying to emails may prefer this as their primary communication method. Alternatively, you could forward the customer’s reply to a monitored email alias.” 

 

 

 

 

 

 

 

 

 

 

 

 

The setup part is a simple technical check on their end, where they look for a fully authenticated domain and an MX record. They likely won’t know if you’ve responded or not until they begin to see an increase in complaints (i.e., people marking your email as junk or spam), which will lead to deliverability issues. Industry chatter also suggests that a high bounce rate will likely raise their eyebrows and get them to investigate your practices more granularly. In this scenario, maintaining list hygiene becomes paramount. Ensure to immediately remove subscribers who complain, consistently validate your subscriber list, and pay careful attention to engagement metrics. 

Microsoft on unsubscribing and transparency 

An unsubscribe link is not only legally required under laws like CAN-SPAM and GDPR, but its presence (or absence) also serves as a strong deliverability signal for inbox providers. If your emails lack an unsubscribe link, you’re raising a red flag even before your message is read. If you’re unsure about this, it might be the right time for a comprehensive review of your email program. We’d be happy to help. 

But what about the one-click unsubscribe? Although at this time Microsoft does not require it, they do support it. They also expect you to have a visible, easy way for subscribers to opt out. If people want to leave your program, let them! Microsoft also expects you to honor this request immediately.  

We talked about list hygiene and bounces, so let’s move to the transparency piece. Microsoft says to use accurate subject lines, avoid deceptive headers, and ensure your recipients have consented to receive your messages. So basically, don’t try and bait and switch your subscribers with a subject line that doesn’t directly relate to the content.  

I could talk all day about why actually obtaining your subscribers consent prior to sending marketing emails is so important but will spare you here and instead invite you to read “A Marketer’s Guide to Opt-in Best Practices” written by my esteemed colleague, Rafael Viana.

How do Microsoft’s requirements stack up with Gmail and Yahoo?  

It’s probably a good idea to see how Microsoft is the same or different from other major providers.  

Requirement	Microsoft	Gmail	Yahoo
Bulk sender volume	5,000+/day	5,000+/day	Around 5,000+/day but not specified
SPF	Required	Required	Required
DKIM	Required	Required	Required
DMARC	Required. Policy=none is permitted	Required. Policy=none is permitted	Required. Policy=none is permitted
Spam rate	Undefined	0.3% or below	0.3% or below
One-click unsubscribe (RFC 8058)	Supported but not required.	Required	Required
Visible unsubscribe	Required	Required	Required

 

Building a better inbox experience

While it may feel like mailbox providers are tightening the screws on marketers, the real pressure is being placed where it belongs—on bad actors. These evolving requirements aren’t meant to slow down legitimate senders; they’re designed to protect the inbox and the people behind it. By embracing authentication protocols and visible opt-out standards, we’re not just complying—we’re actively helping to keep email a trusted and effective channel. At the end of the day, it’s about putting subscribers first and safeguarding the relationships we’ve worked so hard to earn. 

Want more insights into Microsoft’s requirements? Curious to hear what Gmail and Yahoo think about them? Check out our State of Email Live webinar when all three MBPs joined our panel discussion!