Microsoft is increasing security requirements for high volume senders. Here’s how to prepare.
Microsoft is making big moves to tighten email security on its Outlook email platform. Following Google and Yahoo’s 2024 changes, Microsoft will begin enforcing stricter authentication requirements for high-volume senders on Outlook and Hotmail, requiring compliance with SPF (Sender Policy Framework), DKIM (DomainKeys Identified Mail), and DMARC (Domain-based Message Authentication, Reporting & Conformance) security protocols.
Why the change? Simply put, email remains one of the most common and popular forms of communication and verification. Microsoft is doubling down on email security and trust as online security becomes increasingly important due to emerging cyber attack methods. By enforcing these authentication standards, Microsoft aims to reduce phishing, spoofing, and spam, making Outlook inboxes safer for millions of users.
This shift has long been predicted and should serve as a wake-up call for businesses that rely heavily on Outlook (or any email), especially organizations that regularly interact with consumers. Stronger authentication is the new norm, and senders who don’t adapt will risk deliverability issues.
In this article, we’ll break down exactly what’s changing, the technical details behind DMARC, DKIM, and SPF, what you need to do, and why these updates are a healthy change for both senders and recipients.
New Email Sender Requirements Include DMARC, DKIM, and SPF
The new Microsoft Outlook email requirements mean that any sender sending over 5,000 emails per day must implement proper email authentication. All emails must pass checks for SPF, DKIM, and DMARC, which are three key protocols that verify an email’s legitimacy to prevent phishing and spoofing. Senders that fail to comply will see their messages rerouted to junk folders from May 5, 2025, with stricter enforcement, or outright email rejection coming later.
Additional Recommendations for high volume senders
Microsoft encourages high-volume senders to adopt best practices for email deliverability, beginning with the use of valid sender addresses in both the ‘From:’ and ‘Reply-To:’ fields. To ensure user satisfaction and protect consumer rights, bulk and marketing emails should also include clear unsubscribe options. Senders are advised to regularly clean their email lists to remove inactive addresses, improving engagement and reducing bounce rates. EasyDMARC’s Email Verifier tool can assist with validating email lists and maximizing deliverability.
Additionally and in line with email hygiene recommendations, Microsoft is stressing the importance of transparent messaging, including honest subject lines and explicit recipient consent, warning that failure to adhere to these guidelines may result in email filtering or blocking.
New Requirements for Sending Emails to Microsoft, Google, Apple, and Yahoo: The Ultimate Guide to email security protocols
The regulations imposed by all four major email platform providers are:
- SPF, DKIM Authentication
- DMARC Implementation (p=none)
- DMARC Alignment
- Valid rDNS (PTR)
- TLS Encryption
- Spam Complaint Threshold
- List-Unsubscribe Header & One-Click Unsubscribe
- Unsubscribe Processing Timeline
- Valid “From” & “Reply-To” address
- Bounce Handling & List Hygiene
Here’s a breakdown of the key requirements and technical expectations senders need to know about:
| Requirement | Yahoo | Microsoft (Outlook) | Apple (iCloud Mail) | |
| SPF Authentication | Required (All Senders) | Required (All Senders) | Required (Bulk Senders only) | Required (Bulk Senders) |
| DKIM Authentication | Required (All Senders) | Required (All Senders) | Required (Bulk Senders only) | Required (Bulk Senders) |
| DMARC Implementation | Required for Bulk (p=none OK) | Required for Bulk (p=none OK) | Required for Bulk (p=none OK) | Required for Bulk Senders |
| DMARC Alignment | Required for Bulk | Required for Bulk (Relaxed OK) | Required for Bulk (prefer SPF & DKIM aligned) | Not specified |
| Valid Forward and Reverse DNS (PTR) | Required (All Senders) | Required (All Senders) | Not mentioned | Required (Bulk Senders) |
| TLS Encryption | Required (All Senders) | Not mentioned | Not mentioned | Not specified |
| Spam Complaint Rate | Must be < 0.3% (Postmaster Tools) | Must be < 0.3% | Not specified | Not specified |
| One-Click Unsubscribe | Required for Bulk | Required for Bulk | Recommended | Required for Bulk Senders |
| List-Unsubscribe Header | Implied by one-click requirement | Required (mailto: or POST) | Recommended | Not specified |
| Unsubscribe Processing Timeline | Not specified | Must honor within 2 days | Not specified | Immediate |
| Valid “From” / “Reply-To” Addresses | Required | Required | Required for Bulk | Required for Bulk Senders |
| Bounce Handling / List Hygiene | Required | Expected for deliverability | Recommended for Bulk | Required for Bulk Senders |
If you’re unsure about what these requirements mean for you as a sender, here is a guide to what these terms mean and how you can implement them for your organization. If you already know about these email security protocols, click here to skip the terminology.
SPF, DKIM Authentication
SPF (Sender Policy Framework) is a DNS TXT record that declares which IP addresses or hostnames are authorized to send emails on behalf of a domain. This is tied to the RFC5321.MailFrom, also known as the envelope sender. SPF validation is done by checking the return-path domain against the connecting IP.
To set up SPF, analyze your DMARC aggregate reports, investigate the sending sources used, and adjust your SPF record to allow the necessary hostnames and IP addresses using EasyDMARC’s SPF Generator tool.
DKIM (DomainKeys Identified Mail) is a mechanism to digitally sign emails using asymmetric cryptography. The sender signs the message with a private key, and the recipient verifies the message with the public key which is published in the DNS. DKIM signs headers and parts of the body to ensure the content wasn’t tampered with.
SPF and DKIM make sure the message is authenticated, but they cannot provide protection for the domain used in the ‘from’ address; that’s where DMARC and alignment come in.
Note: The best approach to adjusting your SPF and DKIM records is to analyze your DMARC aggregate reports to understand all the sources sending on behalf of your domain. These reports help you identify authorized and unauthorized senders by IP address. However, reviewing raw DMARC XML files can be complex, as they often lack readable source names. EasyDMARC can convert this complex data into readable source names, making it easier to track and configure authorized senders. You can also use EasyDMARC’s Email Source Configuration tool to get direct links to vendor documentation and our Knowledge Base articles to guide you in correctly setting up SPF and DKIM.
DMARC Implementation (p=none)
DMARC (Domain-based Message Authentication, Reporting & Conformance) is a protocol that builds on SPF and DKIM to give domain owners control over what happens when authentication or alignment fails. It also provides visibility into your domain’s email traffic through reporting.
All major email platform providers require a p=none policy. This is the monitoring mode of DMARC and represents the first step in a domain’s DMARC journey. These providers do not currently require a RUA (Reporting URI for Aggregate reports) tag, but it’s strongly recommended.
Why a RUA Tag Is Recommended
Without a RUA tag, domain owners have no visibility into who is sending emails on their behalf. DMARC reports sent to an address utilizing a RUA tag can identify misconfigurations in SPF or DKIM, unaligned senders, and spoofing attempts. These reports are essential for analyzing alignment, understanding real-world email behavior, and moving toward enforcement (p=quarantine or p=reject).
Note: The p=none designation is a monitoring mode, not enforcement, but it’s still the safest way to begin DMARC implementation. DMARC works at the domain level, so even one misconfigured service can lead to mail delivery issues. With p=none, you’re able to observe authentication and domain alignment without risking mail loss. As you understand your authentication and alignment more, you can move towards implementing p=reject. EasyDMARC helps by offering segmentation, traffic classification, source validation, and policy recommendations, so you can enforce safely.
DMARC Alignment
DMARC requires domain alignment between the domain in the ‘from’ header (RFC5322.From) and the domains used either SPF (RFC5321.MailFrom) or DKIM (d= tag in signature). Alignment can be either relaxed by default or strict. Default means subdomains are allowed (mail.example.com can align with example.com), while strict requires domains to match exactly. At least one of SPF or DKIM must both pass and align for DMARC to pass.
Note that some providers handle bounce messages using their own return-path, which breaks SPF alignment. In those cases, DKIM alignment becomes critical.
Note: Passing SPF or DKIM doesn’t mean DMARC will pass. For DMARC to pass, your domain (From:) needs to align with the domain used in SPF (Return-Path) or DKIM (d=).
For example, if you’re using SendGrid but haven’t set up your own domain’s SPF and DKIM their default will be set to sendgrid.net. SPF and DKIM may pass, but alignment will fail, and so will DMARC. Email service providers provide CNAMEs setups to fix alignment and make DMARC work on your domain.
Valid rDNS (PTR)
The sending IP must have a valid PTR record (reverse DNS), meaning that the IP should resolve to a fully qualified domain name, and that domain should resolve back to the same IP address. This requirement applies mainly to senders using self-hosted MTAs and dedicated servers or IPs.
Cloud-based email services like Gmail or Microsoft 365 have this requirement handled, but if you’re managing your own MTA, not having a proper rDNS setup can be a red flag for spam filters. If you’re using well-known providers like Google, Microsoft, or Yahoo, they will handle rDNS.
TLS Encryption
TLS (Transport Layer Security) encryption makes sure that emails are encrypted during transmission between sending and receiving servers. Where SPF, DKIM, and DMARC verify the sender’s identity, TLS secures the delivery path by preventing interception and tampering.
- Providers like Google, Yahoo, Microsoft, and Apple expect all senders to support TLS encryption during transmission.
- Your mail server must offer and accept secure TLS connections when sending and receiving email.
- TLS enforcement is different, and involves MTA-STS (Mail Transfer Agent – Strict Transport Security).
MTA-STS allows domain owners to ensure incoming emails are only accepted if sent over a secure TLS connection. If TLS cannot be established, the message will be rejected or deferred based on the policy. This prevents downgrade attacks and ensures encrypted delivery by default.
TLS-RPT (TLS Reporting)
TLS reporting provides reports on successful and failed TLS negotiations. It helps identify misconfigurations, invalid certificates, or gaps in secure delivery. EasyDMARC offers a one-click setup for MTA-STS and TLS-RPT so you can collect and process TLS reports to help you monitor and fix delivery issues.
Note: Most ESPs already have TLS enabled, but if you’re running your own mail servers, make sure STARTTLS is properly configured. Email without TLS is like shouting your message across a crowded room — anyone can listen.
Spam Complaint Threshold
Mailbox providers are now actively monitoring spam complaint rates with a maximum allowed threshold of 0.3%. This means that if you send 1,000 emails, you must receive fewer than 3 complaints.
Spam complaints are user-generated, meaning they occur when a recipient manually clicks “Report as spam.” They are not related to technical bounces. Maintaining a healthy complaint rate involves only sending to opted-in recipients, honoring unsubscribe requests, and using consistent sender identity and content.
You can use the Google Postmaster integration in our EasySender platform to monitor your spam complaint rate and other important parameters
Note: Spam complaint thresholds are one of the most difficult things to control. Gmail, Outlook, and Yahoo all have their own thresholds. Keeping a spam rate under .10% is recommended, though most industry players agree that you need to stay under 0.3% to avoid deliverability issues. That’s 3 complaints per 1,000 emails — per provider, not overall. If you’re getting too many complaints, you’re either targeting the wrong audience or not segmenting your lists properly. Make sure to review your email strategy and hygiene.
List-Unsubscribe Headers and One-Click Unsubscribes
Gmail, Yahoo, Microsoft, and Apple all recommend or require marketing and bulk senders to support one-click unsubscribes via headers, not just links inside the email body. This feature enables email clients to display a native unsubscribe button next to the sender in the user interface.
To comply, two headers must be included:
List-Unsubscribe: <mailto:[email protected]>, <https://yourdomain.com/unsubscribe>
List-Unsubscribe-Post: List-Unsubscribe=One-Click
- The List-Unsubscribe header provides one or more unsubscribe methods: a mailto: or HTTPS link.
- The List-Unsubscribe-Post header tells the client that the HTTPS endpoint supports one-click HTTP POST unsubscribe.
Google in particular explicitly requires both headers. If List-Unsubscribe-Post is missing, Gmail won’t trigger one-click unsubscribe. The HTTPS link in the List-Unsubscribe header must respond to a POST request without redirects or confirmation pages. Failing to support this properly will increase your complaint rate, and Gmail will treat the sender as non-compliant.
Note: Beyond appearing legitimate, Unsubscribe headers and one-click unsubscribes are about avoiding spam complaints. Adding List-Unsubscribe headers helps mailbox providers identify you as a safe sender, with Gmail supporting ‘one-click unsubscribe,’ which users can trigger directly from the interface. This improves trust and reduces frustration.
Note: If you use the same ‘From:’ address for both marketing and transactional emails, unsubscribing from one might block the other. Segment your sender addresses accordingly.
Unsubscribe Processing Timeline
In addition to one-click unsubscribe support, email service providers are enforcing unsubscribe processing deadlines. Yahoo requires senders to honor unsubscribe requests within two business days while Apple iCloud requires near-immediate action. Gmail and Outlook tracks whether senders honor unsubscribe requests in a timely manner, but do not specify any timeframe.
The header must be present, and unsubscribes must be automatically and reliably handled. Failing to process requests promptly can lead to compliance violations and increased complaint rates.
Note: Despite Yahoo offering two business days and others not specifying a timeline, best practises dictate processing immediately. Some ESPs let you customize suppression logic while others enforce it instantly. If you’re running your own system, your unsubscribe logic must take effect immediately or you risk getting marked as spam, which is significantly worse. If someone unsubscribes and still receives email, even by accident, that’s a red flag for your domain reputation.
Valid ‘From:’ and ‘Reply-To:’ Address
The ‘From:’ and ‘Reply-To:’ headers must use valid, routable, and monitored email addresses. They must not bounce, they should be able to receive replies and they should be actively monitored by support or marketing teams. Using invalid or non-existent reply addresses can damage trust and trigger delivery failures or spam filtering.
Note: Using no-reply@ is now outdated and can hurt engagement. Always use a real email address in your From: and Reply-To: headers and continuously monitor it. It shows you’re open to feedback and improves your trust score.
Bounce Handling and List Hygiene
Proper bounce handling is important for reputation management. Hard bounces where the user is not found must result in immediate removal from future sends. Soft bounces, where the email was delivered properly but could not enter the receivers mailbox due to other reasons (server failures, full inboxes, message was too long, etc.) should be tracked and monitored; repeated soft bounces should be temporarily suppressed.
List hygiene stipulates removing inactive users, avoiding purchased or scraped address lists, and confirming opt-ins. Sending to outdated or unverified lists increases bounce rates, spam complaints, and reduces engagement, all of which negatively affect inbox placement.
Note: If you’re using an email service provider, bounces are auto-handled. If you’re self-hosting, you need to track hard and soft bounces, as ignoring hard bounces can destroy your sender score. Implement a sunset policy by removing users who haven’t opened an email in 90 to 180 days. A bloated list looks good for numbers but hurts deliverability. It’s better to have 1,000 engaged users than 10,000 inactive ones.
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Steps for Businesses to Secure Email Deliverability in Outlook
With Microsoft enforcing stricter authentication rules, businesses must take proactive steps to comply with these changes or risk encountering email deliverability issues. If your domain lacks DMARC, SPF, or DKIM, it’s time to get started. Here’s a step-by-step guide to ensure your emails remain secure and deliverable.
1. Check Your Current Email Authentication Setup
Before making changes, assess your domain’s authentication records. Many organizations unknowingly operate with missing or misconfigured SPF, DKIM, or DMARC settings, leading to failed email deliveries or security risks. Start by using our DMARC checker to verify whether your domain has a DMARC policy in place.
2. Set Up and Verify SPF Records
Without a valid SPF record, Outlook may flag your emails as suspicious. EasyDMARC’s SPF lookup can check whether your domain has an SPF record. If it doesn’t, update your DNS to include only authorized mail servers. Be wary of SPF’s 10 DNS lookup limit, as exceeding this can affect your authentication.
Our Easy SPF tool can easily solve this lookup limit, as well as give you centralized SPF management.
3. Implement DKIM
Without DKIM, recipients can’t verify whether an email truly came from you. You can check your DKIM setup with our DKIM checker. If it’s missing, generate a DKIM key and publish it in your DNS to sign your outgoing emails properly.
4. Enable DMARC and Set Up RUA Reports
Once SPF and DKIM are in place, implementing DMARC strengthens email security by defining how unauthenticated emails should be handled. Start with a DMARc policy of p=none, so your email deliverability is not affected.
A key part of this is enabling RUA (Reporting URI for Aggregate Reports), which gives you visibility into how your emails are processed by specifying an email address your aggregate reports can be sent to. Aggregate reports help you to identify authentication failures, detect unauthorized use of your domain, and optimize your security policies based on real-world data.
5. Monitor and Adjust Your DMARC Policy
Over time, you must tighten your email security by moving to a DMARC policy of p=quarantine, where suspicious emails go to spam, and eventually p=reject, where unauthorized emails are blocked completely. P=reject is the golden standard for email authentication.
By taking these steps now, and learning how to set up DMARC, businesses can avoid disruptions when Microsoft enforces these requirements on May 5, 2025, ensuring emails reach inboxes while keeping their domains secure.
EasyDMARC Makes DMARC Implementation Easy
As Microsoft Outlook adopts this latest security measure, EasyDMARC can help you stay compliant. EasyDMARC makes DMARC authentication simple with our intuitive platform, which is designed to streamline the entire DMARC implementation process for businesses.
Our DMARC engineers can help you set up DMARC, SPF, and DKIM correctly, ensuring your domain’s email authentication is correctly implemented. With our user-friendly interface, even organizations with limited technical knowledge can quickly get their email systems aligned with email security best practices. Our platform features, like real-time alerts and detailed reports, keep you informed about any issues that might affect your email reputation before they become problems.
New Outlook Requirements Reveal A Need For Increased Security, Transparency
It’s clear that email security is becoming non-negotiable for more email security providers. The move towards enforcing protocols like SPF, DKIM, and DMARC aims to reduce phishing, spoofing, and spam, making email safer for everyone. For businesses, this means adapting to new industry standards, improving deliverability, and protecting your brand’s reputation.
At EasyDMARC, we believe in a bright future for email. Our mission is to ensure your business or organization’s security in cyberspace, helping you navigate these changes and maintain trust with your recipients. The upcoming changes from Microsoft may seem a bit daunting, but they’re actually a step toward better, safer email for everyone. With the right tools and support, this process can be simple, fast, and easy.
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