The inbox has a landlord. Here are the house rules for your email.

Say you run a gym with six locations, and on Monday you send a spring offer to your whole list. You wrote it. You paid for the email platform. The list is yours. From the moment you hit send, though, most of what happens next is decided by somebody else: whether the mail is accepted, which tab it lands in, where in that tab it sits, what paid message sits above it, and whether your member reads your words or a summary of them.

For everyone on your list with a Gmail address, that somebody is Google. Google says 3 billion users rely on Gmail. We use it ourselves, and so do most of our clients. Google publishes most of its rules, so this part is mostly a reading of them. When you send email to Gmail, you are a tenant, and it helps to read the lease.

In Part 2 we read Google's new wording on Gmail and ads. Here is everything else the landlord sets.

Google writes the sender rules

On October 3, 2023, Neil Kumaran of Gmail's security team announced new requirements for bulk senders, "those who send more than 5,000 messages to Gmail addresses in one day." By February 2024, they had to authenticate their email, let people unsubscribe in one click and process that request within two days, and stay under a spam-rate threshold.

Google's current Email sender guidelines spell out the details. Every sender, of any size, must set up SPF or DKIM authentication and keep spam rates reported in Google's Postmaster Tools below 0.3%. Bulk senders must also align their From domain for DMARC and support one-click unsubscribe on marketing mail. Google recommends staying below 0.10%. Mail from senders that miss the rules, the page says, "might be marked as spam."

Source: Google, Oct. 3, 2023; Gmail Help, Email sender guidelines

These rules are reasonable, and they cut spam. They are also one company's rules, enforced by that company, for the inbox most of your customers use. A multi-location brand with a large list can cross the bulk line on a single campaign day.

Google ranks the Promotions tab, and sells a slot in Gmail

Once mail is accepted, Gmail sorts it. Most marketing email lands in the Promotions tab, and inside that tab, Google's developer page says, "Gmail automatically groups and highlights emails in the Promotions tab that people are most likely to engage with." Senders can add annotations such as deal details and images. Google says those "are not ads and happen automatically based on a number of factors." It does not publish the factors, and it does not promise any annotation will show.

Gmail is also ad inventory. Google Ads Help describes Demand Gen campaigns as ads that run "across YouTube (including Shorts), Discover, Gmail, Maps, and the Google Display Network." So the company that ranks your promotion in Gmail also sells ad space inside Gmail to other advertisers, including a competitor down the street.

And Gmail helps readers leave. Since July 2025, rolling out in select countries, a Manage subscriptions view lists senders "sorted by the most frequent senders" with a one-click unsubscribe. In January 2026, Google said Gmail "synthesizes the entire conversation into a concise summary of key points," a feature "rolling out today for everyone at no cost."

1. 1The gateSender rules decide whether Gmail accepts it
2. 2The tabGmail files it, usually in Promotions
3. 3The rankingGmail decides what to group and highlight
4. 4The slot aboveAn ad can sit at the top of that tab
5. 5The summaryThe reader may see a summary before your words

What is documented, and what is not

Everything above comes from Google's own pages. What is not documented is any claim that Gmail holds down a particular brand's mail on purpose. We do not claim it. Inbox placement is automated and mostly unexplained, which is a reason to measure your own results rather than guess at motives.

Google itself says not to lean on the number most senders watch:

"Google doesn't track open rates. Google can't verify the accuracy of open rates reported by third parties."

What a local business can do

Paying more for email does not move the landlord. The fixes are cheaper and more boring than that, and they work for a two-location studio as well as a 40-location franchise.

1. Authenticate your sending domain

   Ask your email platform to set up SPF, DKIM and DMARC for the domain you send from, and check them in Google's Postmaster Tools. This is the entry ticket, and it is free.

2. Keep one-click unsubscribe on every marketing email

   Make leaving easy. A member who cannot find the exit marks you as spam, and your spam rate is the number Gmail enforces.

3. Put the offer in the first line

   Price, what is included, the end date and the location, in plain text near the top. If a summary or a preview is all your member sees, it should still carry the offer.

4. Judge email by bookings and replies

   Count classes booked, consultations scheduled and replies from the link in each email. Google says it doesn't track open rates and can't verify the ones third parties report.

We wrote about the summary side, and what survives it, in Your email gets read by an agent first. For counting results when the inbox and the agents in it keep changing, see Measuring marketing when agents shop.

Next, in Part 4, we leave the inbox for the website and read what Amazon's robots.txt lets in and keeps out.

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Sources

• Google, Neil Kumaran, "New Gmail protections for a safer, less spammy inbox," October 3, 2023. blog.google
• Google, Gmail Help, "Email sender guidelines," read October 24, 2026. support.google.com
• Google for Developers, "Gmail Promotions tab annotations." developers.google.com
• Google Ads Help, "About Demand Gen campaigns." support.google.com
• Google, Chris Doan, "Declutter your inbox with Gmail's newest feature," July 8, 2025. blog.google
• Google, Blake Barnes, "Gmail is entering the Gemini era," January 8, 2026. blog.google