As a webmaster, I’ve been crushed by Microsoft Deliverability issues, with their S3140 error—“part of their network is on our block list”—blocking my RicheyWeb server’s 1–5 weekly emails to outlook.com, hotmail.com, live.com, and countless business domains hosted by Microsoft.
A Spamhaus blacklist on an IPv6 /64 subnet, spanning an absurd 18 quintillion addresses (2^64), forced me to a switch to IPv4, but Microsoft’s private blacklist didn’t budge. Desperate, I tried SendGrid, expecting better Microsoft Deliverability. Same S3140 error, same bounces, no help without a costly upgrade, and no access to their IP data. Hosting with Google or Microsoft might improve deliverability, but their Terms of Service (ToS) admit they’ll snoop on your emails—a privacy dealbreaker. Webmasters, you know this trap: Microsoft’s fortress, SendGrid’s false promises, and big tech’s spying. Here’s why Microsoft Deliverability has no magic bullet—and how to fight back by denying Microsoft-hosted emails, with a sneak peek at a RicheyWeb tool to make it easier.
The SendGrid Experiment: No Fix for Microsoft Deliverability
Hoping to solve RicheyWeb’s Microsoft Deliverability issues, I turned to SendGrid, expecting their managed infrastructure to ensure delivery. Their shared IPs, touted as a robust solution, promised better Microsoft Deliverability than my self-hosted server. The result? A mirror of my RicheyWeb failure: the same S3140 error—“part of their network is on our block list”—blocked every email to Microsoft-hosted domains, from outlook.com to custom business addresses. No improvement, no answers.
Why did SendGrid fail? Their shared IPs, used by countless users, are a liability. If one user sends to a spam trap or racks up complaints, the entire IP pool’s reputation tanks, triggering Microsoft’s blacklist. I couldn’t access Microsoft’s Smart Network Data Services (SNDS) to check complaint rates or spam trap hits—SendGrid locks that data to themselves. Support was useless without a Pro or Premier plan (starting at $89.95/month). When I pressed for help, they offered no insight into their IP status, leaving me stranded. X users like @JudahGabriel (2025) lament SendGrid’s limits for small projects, and a 2020 Krebs on Security report flagged hacked SendGrid accounts fueling spam, tanking shared IP reputations. My experiment proved SendGrid’s no better than self-hosting for Microsoft Deliverability.
SendGrid: "Hi, we're killing off your free plan and will delete your contacts in 60 days."
— Judah Gabriel 🇮🇱 (@JudahGabriel) May 27, 2025
I use SendGrid for simple side projects and 501c3 non-profit work for email confirmations, password resets, etc. Maybe 400 emails/month.
60 days is nowhere near enough time to migrate… https://t.co/TCnaEzWnnS
Spam: The Root of Microsoft Deliverability Woes
Emails hit spam or bounce due to poor sender reputation, spammy content, or spam traps (inactive emails designed to catch spammers). Microsoft’s SmartScreen and connection filters are merciless, favoring high engagement and perfect authentication. Low-volume senders like me, with 1–5 emails a week to Microsoft domains, can’t build a reputation, making us easy targets for Microsoft Deliverability blocks. My plain-text emails, free of trigger words, still bounced, showing reputation often trumps content.
SendGrid’s failure underscores this. Shared IPs inherit the worst users’ sins—spam complaints or trap hits drag everyone down. My experiment showed SendGrid’s shared IPs landed in the same S3140 trap as my RicheyWeb server. Even dedicated IPs (costly add-ons) need careful warm-up and maintenance, offering no guarantees for Microsoft Deliverability.
Blacklists: 18 Quintillion Addresses vs. Microsoft’s Wall
Blacklists flag IPs or domains for spam, and Microsoft Deliverability heavily depends on them. Public blacklists like Spamhaus are fixable but can be outrageously broad. My RicheyWeb server was swept into an IPv6 /64 subnet blacklist—a staggering 18 quintillion addresses (2^64, or 18,446,744,073,709,551,616), enough to assign an IP to every grain of sand on Earth—likely due to another user’s spam. Switching to IPv4 cleared Spamhaus, but Microsoft’s private blacklist, covering consumer domains (outlook.com, hotmail.com, live.com) and countless business domains hosted via Microsoft 365 or Exchange Online, is a nightmare. Microsoft blocks IPs based on secret criteria like user complaints or spam traps, often hitting entire ranges.
My IPv4 IP, despite sending only 1–5 emails weekly, remains blocked with S3140. Delisting via
Many people are asking me to name and shame, so I will do it:
— Carlos Fenollosa (@cfenollosa) September 4, 2022
Microsoft. I have been unable to deliver a single email to a Microsoft server in the past five years.
live-dot-com, outlook-dot-com, and any organization using Office 365 as their email server. It goes to /dev/null
Privacy vs. Microsoft Deliverability: A Brutal Trade-Off
Google or Microsoft hosting might sidestep S3140, boosting Microsoft Deliverability, as their IPs rarely face blocks. But their ToS are a privacy disaster. Google’s (policies.google.com/terms) permits email scanning for ads and analytics, while Microsoft’s Services Agreement (microsoft.com/en-us/servicesagreement) allows it for “security, safety, or reliability.” Their history—Google’s 2018 data leaks, Microsoft’s 2021 Exchange breaches—screams distrust. For webmasters handling client or proprietary data, handing over emails to these giants is unthinkable. Self-hosting, like RicheyWeb, keeps control but means battling Microsoft Deliverability issues.
SendGrid’s no privacy haven either. Their parent company Twilio faced 2020 and 2021 security lapses, with hacked accounts sending phishing emails, per Krebs on Security. My SendGrid experiment showed it’s no better than self-hosting for Microsoft Deliverability, and it’s no safer for data. Paying for a higher-tier plan might get a dedicated IP, but it’s still within their ecosystem, with no privacy guarantees.
Solution: Deny All Microsoft-Hosted Emails
Microsoft Deliverability is a deliberate roadblock, unfairly targeting small senders while favoring their own and Google’s hosted services. Their delisting process is opaque, their filters unforgiving, and their support nonexistent for low-volume senders like me. Microsoft hosts not just consumer domains (outlook.com, hotmail.com, live.com) but countless business domains via Microsoft 365 and Exchange Online, where custom domains (e.g.,
The only way to force change is to make all Microsoft-hosted emails toxic to webmasters by denying them access to your services. By probing MX records, you can identify and block any email address—consumer or business—hosted by Microsoft, pressuring them to rethink their draconian filters. To simplify this, I’m developing a free RicheyWeb project: a PHP library and Joomla extension that blocks registration and contact form submissions for email addresses failing an MX record check. It’s not limited to Microsoft but includes configurable options to block their hosted domains, empowering webmasters to tackle Microsoft Deliverability head-on. Here’s how to implement the strategy now:
Probe MX Records
When users sign up for your service or submit a contact form, check their email’s MX record using a DNS lookup (e.g., dig mx yourcompany.com or libraries like Python’s dnspython).
If the MX record points to Microsoft servers (e.g., mx1.hotmail.com, mx2.hotmail.com, outlook-com.olc.protection.outlook.com, or [domain]-com.mail.protection.outlook.com), reject the submission. Inform users to use a non-Microsoft email, citing Microsoft’s unfair blacklisting practices that sabotage Microsoft Deliverability. This strategy sends a powerful message: if Microsoft blocks your server with no recourse, their users—whether on outlook.com or a custom business domain—lose access to your services.
By making all Microsoft-hosted emails liabilities, unusable for website registrations or contact forms, webmasters can collectively pressure Microsoft to prioritize Microsoft Deliverability or risk their email domains becoming pariahs.
Joomla Extension Sneak Peak: User - MX Filter
Stay tuned for the RicheyWeb PHP library and Joomla extension, which will automate this MX check with configurable blocking, allowing Microsoft-specific blocking, giving you a plug-and-play tool to reclaim control over Microsoft Deliverability. This will offer similar functionality to my recently released Contact - Valid Email plugin.
Conclusion: No Easy Wins, Just Hard-Won Control
My SendGrid experiment was a complete dud—same S3140 error as my RicheyWeb server, no support, no way to diagnose their blacklisted IPs. Spamhaus’s 18 quintillion–address blacklist was a hurdle I cleared, but Microsoft’s private blacklist and Google’s privacy invasions are tougher foes. Google and Microsoft might improve Microsoft Deliverability, but their ToS admit they’ll snoop, and their scandals prove they can’t be trusted. Denying all Microsoft-hosted emails—consumer and business—via MX record checks is the only way to fight back—make their domains a liability until Microsoft Deliverability plays fair. Watch for my upcoming RicheyWeb PHP library and Joomla extension to simplify this fight. Stick to self-hosting for control, and don’t let Microsoft’s fortress or big tech’s spying win.
