Sending bulk emails such as newsletters, promotions, or notifications is a common practice for many companies and organizations.
However, ensuring those messages reach the inbox and don’t end up in the spam folder (junk mail) depends on meeting certain requirements set by the major email providers.
More than requirements, we could consider them best practices to prevent the world from being flooded with spam.
Outlook (Microsoft’s email service, formerly Hotmail/Live) recently announced new requirements for high-volume senders, following similar measures introduced by Gmail and Yahoo! in 2024.
Also keep in mind that at Mailrelay, we help you set up these configurations correctly to boost your results.
Outlook: new authentication requirements for bulk mailers
Outlook.com (which enincludes @outlook.com, @hotmail.com, @live.com and other addresses) is tightening its policies to protect users from spam and phishing.
Starting in May 2025, domains sending more than 5,000 emails per day must comply with certain authentication measures.
If your organization sends a large number of emails, Outlook will require you to implement email security protocols, including SPF, DKIM, and DMARC.
· SPF (Sender Policy Framework):
This is a DNS record in your domain that lists which servers or IP addresses are authorized to send emails on your behalf.
Outlook will require the SPF to “match” and approve the message for your sender domain.
In other words, the server from which you send the email must be included in your SPF record; otherwise, the email will fail this validation.
· DKIM (DomainKeys Identified Mail):
This is a system that adds a digital signature to every email you send.
Only the legitimate domain possesses the key to generate that signature.
Outlook now requires DKIM to be set up and the signature to be valid on bulk messages.
This ensures the integrity of the message and confirms it hasn’t been altered along the way.
· DMARC (Domain-based Message Authentication, Reporting and Conformance):
This is a policy you publish in your domain to indicate how emails that fail SPF/DKIM should be handled.
Outlook will require at least one DMARC policy in “p=none” (monitoring only) mode, configured correctly and aligned with your domain.
Alignment means that the domain in the “From” field (the one the recipient sees) must match the domain authenticated by SPF or DKIM.
This prevents someone from sending emails pretending to be from your address.
· What happens if you don’t meet these requirements?
Microsoft announced it will begin redirecting non-compliant messages to the junk mail folder (spam).
In other words, if your domain sends many emails without proper SPF, DKIM, or DMARC, those emails will land in the Junk folder on Outlook.com instead of the inbox.
This measure will begin just after May 5, 2025, giving senders time to adapt.
Later, on a date yet to be announced, Outlook may start rejecting (blocking) those emails entirely if the problem persists.
In short, to avoid Outlook sending your messages to spam, you must authenticate your email with these protocols as soon as possible.
· Along with technical authentication, Outlook strongly recommends maintaining good email marketing hygiene practices when sending emails in bulk
- Valid sender address: ensure the email shown as the sender (the “From:” or “Reply-To:” if different) is valid and functional. It should belong to your actual domain and be able to receive replies. In practice, this means avoiding non-existent “no-reply” addresses or domains you don’t own. A real sender inspires more trust.
- Active unsubscribe link: if you send newsletters or promotions, always include a clear and easy-to-find one-click unsubscribe option. This lets recipients who no longer wish to receive your emails opt out easily. Outlook emphasizes that the link must work properly and be clearly visible.
- List hygiene and bounce management: review your recipient list regularly and remove invalid or inactive addresses. When you send to many addresses that bounce (don’t exist) or to people who don’t remember subscribing, the number of spam complaints will increase. Keeping the list clean reduces wasted messages and user complaints.
- Transparent sending practices: avoid misleading headers or subject lines. Be clear in the subject line about the content and make sure the recipient has consented to receive it. Simply put, don’t send mass emails to people who didn’t request them, and avoid using misleading subject lines – that will only get your messages flagged as spam.
Outlook states that it reserves the right to filter or block senders who don’t comply with these measures, especially if they fail authentication or engage in serious bad practices.
As a result, what should senders do? Review their domain configuration now.
Microsoft advises “get ready now”: audit your DNS records to verify that SPF, DKIM, and DMARC are correctly configured and working.
Gmail: strong authentication, one-click unsubscribe, and spam control
Gmail, Google’s email service, has been fighting spam for years with smart filters, but since 2024 it has gone a step further by setting clear rules for high-volume senders.
Google announced that to keep Gmail inboxes safe and spam-free, it would introduce new requirements for “bulk senders.”
Who qualifies as a bulk sender? Anyone who sends more than 5,000 messages a day to Gmail accounts.
If your domain fits that category, pay attention to what Gmail requires to keep your emails out of the spam folder:
· Authenticate outgoing emails:
Gmail now requires large senders to strongly authenticate their emails following standard best practices.
In practice, this means having SPF and DKIM configured on your domain, and also a DMARC record.
In fact, Google made it clear that high-volume senders must enable both SPF and DKIM (not just one of them), and also have a DMARC record even if it’s set to “none” (monitoring).
This prevents attackers from spoofing your address, as Gmail will verify the email actually comes from servers allowed and signed by your domain.
If your messages aren’t authenticated, there’s a high chance Gmail will flag them as suspicious or not deliver them at all.
· Make it easy to unsubscribe with one click:
Google considers it crucial that users can easily unsubscribe from unwanted emails
That’s why it requires bulk senders to include a one-click unsubscribe option in every commercial email.
Additionally, unsubscribe requests must be processed quickly, within a maximum of two days.
In other words, if a Gmail user clicks “unsubscribe” in your email, you (or your email platform) must remove them from your list within 48 hours to stop sending further messages.
Gmail supports these requirements through open standards that benefit all providers, so once implemented, it’s not just Gmail that benefits, but any email recipient in general.
· Only send emails users expect (and want) to receive:
This point is basically: don’t spam.
Gmail already automatically filters much unsolicited mail, but it has now taken things further by setting a specific spam rate threshold that senders must follow.
In practice, this means that if too many users report your messages as spam, you’ll have problems.
Google didn’t disclose the exact number in its announcement, but sender documentation mentions keeping the spam rate (complaints) below 0.3%.
This means that for every 1,000 emails you send, a maximum of 3 should be flagged as spam by users.
If you exceed that limit, Gmail may take action:
- For example, limit delivery
- Send more of your emails to the spam folder
- Or even block part of your traffic
In fact, Google said that starting in April 2024, it would begin rejecting a percentage of non-compliant emails under the new policies, increasing that percentage over time.
For example, if 25% of your messages are non-compliant (due to missing authentication or high complaint rates), Gmail may start bouncing some of those “problem” emails while letting compliant ones through.
This gradual enforcement approach is designed to push senders to improve without blocking all emails at once.
In short, Google has made mandatory what were previously just good recommendations.
For senders, this means taking several specific actions if they want to maintain good deliverability with Gmail:
· Configure SPF, DKIM, and DMARC on your domain
This is the first step.
If you use an email platform or provider, make sure they’re properly signing your emails on your behalf.
Remember that DMARC only works if SPF/DKIM pass and the domain of the signature or server matches your address (alignment).
That’s why Gmail requires the domain shown in the “From:” field to align with SPF or DKIM.
· Keep your servers in order:
Gmail also notes that sending domains or IPs must have valid reverse DNS (PTR) records and use secure TLS connections.
At Mailrelay, we take care of this part for you, don’t worry.
· Include unsubscribe links and respect them:
Check your mass email templates and make sure to include a visible “unsubscribe” link.
Phrases like “If you no longer want to receive this newsletter, click here” with a working link.
And most importantly: act when someone clicks.
Gmail will check that it’s actually easy to unsubscribe.
If many users mark your emails as “spam” simply because they couldn’t find the unsubscribe option, it will hurt your reputation.
· Maintain the quality of your email list:
Don’t send emails to people who didn’t ask for them.
Avoid purchasing contact lists, as this often leads to reaching users who don’t know you and may mark you as spam.
Run re-confirmation campaigns if your list is old, to ensure people are still interested.
· Google views these practices as “basic email hygiene
In fact, they noted that many legitimate senders were already following most of these requirements, but now they’ll be mandatory for everyone sending in large volumes.
The upside is that implementing these measures boosts your email deliverability: Gmail says that senders who authenticate properly and manage their lists well experience fewer bounces and greater user trust, helping their messages reach more recipients.
In other words, it’s not just about “pleasing Gmail” — it genuinely strengthens your email marketing or communication efforts.
Yahoo!: authentication and respect for the user, the same mission against spam
Yahoo! Mail, which also includes AOL emails and other brands under Yahoo Inc., joined this anti-spam initiative almost simultaneously with Google.
In the first quarter of 2024, they announced that all bulk senders would need to follow new rules to ensure “safer, less spammy email.”
Yahoo’s three key requirements are practically the same three we’ve already seen:
· Authenticate email with secure standards:
Yahoo now requires high-volume senders to use SPF, DKIM, and DMARC on their emails.
Their position is that verifying the sender’s identity is crucial to prevent malicious third parties from impersonating you.
Like Gmail, Yahoo wants you to have at least a published and correctly configured DMARC record, even if it’s in monitoring mode (p=none).
If your emails are not authenticated, they are much more likely to be blocked or marked as dangerous.
In short, Yahoo requires the same on the technical front as the other providers — prove your message is legitimate with these protections on your domain.
· Provide an easy unsubscribe option:
Yahoo emphasizes that its users should be able to stop receiving emails with a single click if they choose.
Although they have long promoted these practices voluntarily, they acknowledge adoption was low, so they decided to make it mandatory.
Specifically, Yahoo requires support for the “one-click unsubscribe” standard and, very importantly, that senders honor the request within a maximum of two days.
This means the same as with Gmail: include the “unsubscribe” link in your emails and process unsubscribes almost immediately.
If a Yahoo/AOL user clicks “I don’t want this email anymore,” you must ensure they are removed from future campaigns within 48 hours.
Yahoo has made it clear that the unsubscribe feature must be fully reliable and seamless for users, with no unnecessary extra steps.
· Only send to those who want your emails:
Yahoo’s (and everyone’s) core philosophy is that the best spam is the one that’s never sent. Therefore, they will monitor and enforce a spam threshold based on user complaints.
Yahoo said they’ve long been measuring spam complaint rates and even sharing that data with trusted senders, but starting in 2024 they’ll begin taking action if someone exceeds a certain limit of unwanted emails.
Although they didn’t disclose an exact number, it’s expected to be similar to Gmail or other providers (i.e., a very small fraction of users flagging your emails as spam).
In practice, what actions does Yahoo take if you send spam?
They can limit the number of emails they accept from your domain, send your messages directly to the spam folder, or even temporarily block your sends if the problem continues.
In fact, Yahoo announced that in February 2024 it would begin enforcing certain standards for all senders, especially authentication and low complaint rates, and would increase enforcement throughout the first half of the year as senders adapt.
By mid-2024, they expect all bulk senders to support one-click unsubscribes and comply with the new rules.
· What should you do if you send many emails to Yahoo or AOL users?
Exactly the same as with Gmail: implement authentication protocols on your domains and follow good sending practices.
Yahoo published a Sender Best Practices guide on its Sender Hub and even offers support contact to help senders adapt.
In summary:
- Set up SPF, DKIM, and DMARC. This is non-negotiable for Yahoo as well. Check your domains using a tool (for example, there are free DMARC checkers) to make sure you have the correct records and that emails are being signed. Yahoo, like the others, will block emails from domains that are not properly identified.
- Send relevant content only to genuine subscribers: Yahoo stresses the importance of sending “only emails our users want.” That means not sending unsolicited emails. You need to have the recipients’ permission (for example, they subscribed on your website or are customers who agreed to receive emails).
- Also, respect the promised frequency: if someone signed up for a monthly newsletter, don’t start sending them daily emails. And of course, don’t buy or sell email lists, as that practice often damages your domain’s reputation because those recipients aren’t expecting your messages.
- Include a clear and working “unsubscribe” option: make sure any Yahoo user can easily opt out. As mentioned, Yahoo requires the user to be removed from your list within two days, so your system must handle this quickly. After that, don’t send them more emails (except perhaps a final confirmation that they’ve been unsubscribed, if applicable). Failing to honor unsubscribe requests not only annoys users but also leads to formal complaints and blocks.
Ultimately, Yahoo has aligned its policy with Gmail’s: mandatory authentication, easy opt-out, and zero tolerance for spam.
Their stated goal is to improve the email experience for all users, and they trust that these measures (along with the cooperation of legitimate senders) will help create safer, more useful inboxes.
Conclusion: Similarities and differences between Outlook, Gmail, and Yahoo
The three major email providers – Outlook (Microsoft), Gmail (Google), and Yahoo (including AOL) – share a common vision: to make email a safer, more reliable, and spam-free channel.
To do this, they are raising the standard for what is expected from senders who send a large number of messages daily.
Generally speaking, there are more similarities than differences in their requirements:
· Sender authentication
This is the fundamental pillar in all cases.
Outlook, Gmail, and Yahoo now require you to prove the identity of your emails through protocols like SPF, DKIM, and DMARC.
What was once “optional” has now become a mandatory requirement when sending high volumes of email.
All three providers expect authenticated emails with aligned domains; otherwise, those messages will likely go to the spam folder or be rejected altogether.
The good news is that once configured, these systems also benefit legitimate senders: for example, they help prevent someone from sending emails pretending to be your company, which protects your brand and your users.
· Facilitating unsubscribe and user control
Another shared point is putting the user in control of what they receive.
Gmail and Yahoo were clear in requiring a one-click unsubscribe feature in bulk emails, with removal to be completed within 48 hours.
Outlook, while presenting it more as a best practice than a strict requirement, emphasizes the same point: a clear opt-out link in your emails.
In the end, they all aim for the same result: if the recipient no longer wants your emails, you must provide an easy way for them to stop receiving them.
This not only avoids frustration but also reduces the chances of your messages being marked as spam (which helps you maintain a good reputation).
In summary, “make it easy to say goodbye” is the shared motto.
· Only send wanted content (avoid spam)
The providers agree that the best email is one the user expects – the kind they look forward to because they subscribed or find it relevant.
That’s why all three are monitoring spam rates and the quality of email lists.
Gmail established a specific percentage (0.3% maximum complaints) as a reference, Yahoo mentioned setting a similar spam threshold, and Outlook warns that it will take action against those who engage in poor sending practices.
In practice, they all want you to avoid sending unsolicited emails: no buying lists, no repeatedly targeting people who no longer engage.
They also share the idea of proactively managing bounces and complaints (for example, removing addresses that always bounce or inactive users).
Don’t worry about this – Mailrelay does it automatically.
The consensus here is clear: if you abuse and send spam, your messages will be filtered or blocked. If you’re responsible and only send to people who asked for it, your chances of reaching the inbox are much higher.
· Industry collaboration:
It’s worth mentioning that these companies are acting in coordination.
Yahoo’s announcement included a quote from Google supporting these measures, and Microsoft’s decision to join in 2025 reaffirms that consensus.
There’s a kind of unified standard in the works: what Gmail and Yahoo started requiring in 2024, Outlook follows in 2025, and likely other providers will adopt as well.
For senders, this means that what you do to satisfy one will serve all.
If you configure SPF, DKIM, and DMARC on your domain and maintain clean sending practices, you’ll be complying simultaneously with Outlook, Gmail, Yahoo, and any other serious email service.
In contrast, if you neglect any of these aspects, you’re likely to face problems across multiple services.
Regarding differences
They essentially boil down to when and how the rules are enforced, rather than the rules themselves.
· Implementation timeline:
Gmail and Yahoo launched their requirements starting in February 2024, with gradual enforcement over the following months (for example, Gmail beginning to reject non-compliant emails in April 2024, Yahoo increasing controls during the first half of 2024).
Outlook, on the other hand, joins a year later: it begins filtering to spam in May 2025 and plans to start rejecting messages later on.
This means that in 2024 Outlook didn’t yet strictly require SPF/DKIM/DMARC for all large senders, but Gmail and Yahoo did; starting in 2025, all three will.
If you’re a sender, the ideal is not to wait: the sooner you adapt, the better – that way, you avoid both present and future problems.
· Initial approach:
Gmail and Yahoo clearly defined the threshold of 5,000 emails per day to their users to consider someone a “high-volume sender”.
Outlook also uses that figure (5,000 daily) to define the large senders subject to this policy.
The difference is that Gmail/Yahoo clearly stated they only count messages sent to their domains (@gmail.com, @yahoo.com, etc.), while Outlook speaks of domains sending 5,000 messages in general (though presumably they are mainly concerned about what reaches Outlook.com).
In any case, the number is similar.
Another small difference is that Gmail already required some authentication even at smaller scales (since 2022–2023 it started filtering messages with no SPF or DKIM), but the new requirement makes it mandatory for high volumes and includes DMARC.
Until now, Outlook allowed perhaps more flexibility for small senders, but is now aiming to raise the standard for large ones.
Essentially, there’s not much discrepancy: all three agree that 5,000/day is the point at which things get very strict, although even if you send less, it’s highly recommended to follow these practices for better delivery.
· Additional technical requirements:
Gmail explicitly mentioned things like using TLS (encrypted email) and configuring PTR records (reverse DNS), while Outlook and Yahoo didn’t highlight this in their communications.
However, these technical details are common best practices across the industry.
It’s not that Outlook doesn’t want them; it likely assumes they’re part of proper server configuration.
Gmail just documented it more thoroughly.
But again, this doesn’t change the essence: a serious sender must use reliable servers with correct DNS and secure connections.
In conclusion, Outlook, Gmail, and Yahoo ask for practically the same things to avoid sending your emails to spam.
They want authenticated and responsible senders.
In summary, to avoid landing in the spam folder, you must:
- Configure authentication (SPF, DKIM, DMARC) on your sending domains – this is crucial for all these platforms.
- Follow best practices with your subscribers: only email those who opted in, make unsubscribing easy, manage complaints — in short, don’t be a spammer, even by accident.
- Give users control: a clear “unsubscribe” link in every bulk email, and respect the user’s decision promptly.
By adopting these measures, you won’t just comply with Outlook, Gmail, and Yahoo’s policies – you’ll also improve the deliverability and trustworthiness of your emails overall.
It’s about sending emails that people want to receive, securely and transparently.
If you succeed, your messages will have a much better chance of landing in the inbox and not the dreaded spam folder.