Hello from Steamboat, Colorado!
I’m wrapping up this newsletter after carving up the mountain all day. 🏂🏼
While I was scanning my Ikon Pass to hop on the gondola, it hit me—email inboxes and ski passes have more in common than you’d think.
Let me explain…
The Ikon Pass is like the golden key to winter wonderland—it gives you access to 60+ legendary ski resorts around the globe. But here’s the thing:
No pass = no ride. No exceptions. You’re not getting past that gate without permission.
Sound familiar?
That’s exactly how email inboxes work. Each email domain (like gmail.com or yahoo.com) is guarded by its own Inbox Service Provider (ISP)—and if they don’t trust you, you're not getting in.
So if you've ever wondered who’s really managing your subscribers’ inboxes or why some emails breeze through while others land in spam purgatory… don’t worry, I’m breaking it all down for you below. ⛷📬
Let’s hit this inbox slope together! 🏔💌
First, you must understand which ISPs power which email domains.
Let’s peel back the curtain and look at who’s managing which inboxes—and what you need to know about each.
Google: Gmail and Beyond
Manages:
@gmail.com
Google Workspace custom domains (e.g., @company.com using Gmail)
Why it matters:
Gmail uses tabs (Primary, Promotions, Social), which affect visibility.
Super sensitive to engagement (clicks, replies).
Tends to clip emails larger than 102 KB.
Yahoo (Now Owned by AOL/Verizon Media)
Manages:
@yahoo.com
@aol.com
@verizon.net
@bellsouth.net
@sbcglobal.net
@att.net
Why it matters:
These older domains often belong to longtime users—great for stable, loyal subscribers.
Yahoo and AOL have merged under Verizon Media, so they often share filtering logic.
Bounce thresholds can be lower (keep under 0.1%)—if you’re sending to bad addresses, they’ll block quickly.
Microsoft (Outlook / Hotmail)
Manages:
@outlook.com
@hotmail.com
@live.com
@msn.com
Some custom enterprise domains via Microsoft 365
Why it matters:
Microsoft has tough spam filters and is quick to block IPs with a poor reputation.
They use Microsoft SmartScreen, which relies heavily on sender reputation and user engagement.
Also popular with corporate users and professionals.
Comcast (Xfinity)
Manages:
@comcast.net
@xfinity.com
Why it matters:
Comcast is strict with authentication and bounce handling.
Their servers tend to throttle unknown or lower-reputation IPs.
Apple iCloud
Manages:
@icloud.com
@me.com
@mac.com
Why it matters:
Apple’s Mail Privacy Protection makes it harder to track opens.
While Apple’s mail client is popular, their mail service isn’t as common as Gmail or Yahoo.
Comcast/Xfinity, EarthLink, and Regional Providers
Also include:
@earthlink.net
@cox.net
@centurylink.net
@rogers.com
Many of these are tied to ISP-provided email services for internet customers.
Why it matters:
Often used by older demographics or people who’ve had their accounts for decades.
Bounce and complaint handling vary widely.
Here is a list of tips to help you hit the inbox, no matter which inbox you are trying to get into.
Keep emails lean and clean (the smaller the amount of data to transfer, the better).
Encourage replies to boost engagement signals.
Avoid too many images or promotional phrases (especially to stay out of the Gmail promotions tab).
Practice good list hygiene (Yahoo especially dislikes bounces, make sure to provide email validation for all subscribers).
Monitor engagement closely (focus on clicks, not opens).
Authenticate your emails (SPF, DKIM, DMARC are a must).
Keep subject lines and preheaders clean—avoid spammy language.
Watch your complaint rate—they don’t tolerate high complaint volumes (shoot for under 0.10%).
Avoid sudden spikes in sending volume (consistency in volume and frequency is key).
Monitor delivery to this domain specifically in your ESP reports.
Postmasters of the Inbox Service Providers
These are the behind-the-scenes gatekeepers of the inbox world for the major ISPs. They manage the rules, filters, and reputation systems that determine whether your emails land in the inbox, the spam folder, or get blocked entirely.
If you're having persistent delivery issues, these postmasters are also the ones you’ll need to reach out to directly—through their official postmaster tools or support channels—to troubleshoot, submit requests, and get back on their good side.
Remember…
Knowing who’s managing your subscribers' inboxes helps you tailor your sending practices, optimize content, and maintain a high deliverability rate.
If you notice that emails to a specific domain consistently underperform, it may not be your content—it could be how the ISP is handling your messages.
Use your ESP’s reporting to track performance by domain—this lets you spot issues early and stay ahead of deliverability challenges.
BEFORE YOU GO
Don’t Let Bad Deliverability Tank Your Email Results
If your emails aren’t landing in the inbox, they’re not doing their job. I’ve seen too many brands struggle with deliverability issues without knowing why.
The truth is, a few key optimizations can make all the difference in getting your emails seen, opened, and clicked.
Happy sending,
Chris Miquel
PS: Want help troubleshooting a specific domain? Hit reply and we’ll take a look with you!
