How Senders Earn Long-Term Inboxing

Mailbox providers like Gmail and Outlook put email from senders they trust in the inbox. This article shows how a new sender earns that trust: start small, send steadily, and protect what you’ve built. It also covers how to recover when your reputation drops.

The reputation scale

Your reputation is how much a mailbox provider trusts email from you. Think of it as a scale from “suspicious” to “highly trusted”.

A new sender starts as unknown. Providers have no history on you: no engagement, no complaints, nothing. Unknown isn’t the same as bad. But providers are careful with strangers. They may throttle your email (accept it slowly), filter it harder, or put more of it in spam until they know you.

You move up the scale by sending email people want, steadily, over time. The catch is that you fall much faster than you climb.

Warming up a new domain or IP

Why you warm up

When you send from a new IP address (the number that identifies your sending server) or a new domain, providers can’t tell you from a spammer. Warming up means starting with small volumes and raising them step by step. This gives providers time to see good signals from you.

Sending a big volume from a new IP or domain on day one is one of the fastest ways to ruin your reputation before you have one.

A warm-up plan

Start with the people most likely to open your email, and widen the audience as volume grows. Here’s a typical plan for a shop, shop.example, moving its newsletter to a new IP:

Weeks	Emails per day	Who you send to	What to watch
1	50–500	People who opened in the last 7–14 days	Bounces, complaints, opens
2	500–2,500	People active in the last 30 days	Complaint spikes, new blocklist listings
3–4	2,500–15,000	People active in the last 60 days	Delivery at each provider, Postmaster Tools
5–8	Up to your full volume	People active in the last 90 days	All numbers holding steady

Treat this as a starting point. A small list may reach full volume sooner. A very large one may need longer.

Warm-up rules

1. Never more than double your volume from one day to the next. If you sent 1,000 yesterday, send no more than 2,000 today.
2. Start with your best readers. Their opens and clicks set a good first impression.
3. Send every day. Don’t send a lot on Monday and nothing on Tuesday. Keep some volume going at weekends too, because long gaps can undo progress.
4. Watch each provider separately. Gmail, Microsoft and Yahoo each warm up at their own pace. Progress at Gmail doesn’t count at Microsoft.
5. Warm up each IP separately. If you have several IPs, each needs its own plan.
6. Slow down when numbers get worse. Fewer opens or more bounces mean you went too fast. Go back a step.

Numbers to watch

These are rough guides, not provider rules:

Number	Healthy	Warning sign
Delivery rate (share of email accepted)	Above 98%	Below 95%
Open rate	Above 25%	Below 15%
Bounce rate (share returned as undeliverable)	Below 1%	Above 2%
Complaint rate (share reported as spam)	Below 0.05%	Above 0.1%
Deferral rate (share told “try again later”)	Below 5%	Above 15%
Blocklists	Not listed	Any listing

Apple Mail can make emails look opened when nobody read them, so open rates run high. Use clicks as a check.

Growing your reputation

After warm-up, building reputation becomes a habit, not a project.

Be predictable

Providers reward steady behaviour. Keep these consistent:

• Volume: roughly the same number of emails day to day and week to week.
• Content: don’t switch from helpful newsletters to pushy sales emails overnight.
• Audience: don’t suddenly mail a large group that has never heard from you.
• Setup: don’t keep changing IPs, domains or ESP (email service provider, the company that sends email for you).

Spammers change things all the time to dodge filters: new domains, sudden bursts, new IPs. So sudden change looks suspicious. You can still grow and change. Just do it gradually, and watch the results.

Good habits build on each other

Reputation grows like interest on savings. When readers engage, your reputation improves. More of your email reaches the inbox, so more people see it, and more of them engage.

The loop also runs backwards. Poor engagement lowers your reputation. More email goes to spam, fewer people see it, and engagement falls further. Small, steady improvements add up over time. So do small problems you leave alone.

Domain reputation and IP reputation

Providers score your domain and your sending IPs separately. You need both, but your domain matters more and more.

Domain reputation:

• Stays with your domain when you change IPs or ESP.
• Reflects all the email you send.
• Is Gmail’s main signal.
• Takes longer to build, but lasts longer.

IP reputation:

• Belongs to one IP address and starts from zero on a new one.
• Matters more at Microsoft than at Gmail.
• Is shared with other senders if you use a shared IP (one that several senders use).
• Changes faster, in both directions.

Build a strong domain reputation first. Then manage your IPs on top: warm them up, watch them, and keep different kinds of email apart.

Protecting what you’ve built

What can damage it

• List decay. Addresses go stale. People change jobs, abandon accounts or lose interest. If you never clean your list, engagement slowly drops.
• Volume spikes. A holiday sale that doubles your usual volume can draw attention, even for a trusted sender. Raise volume over several days before the big send.
• Content drift. Moving away from what readers signed up for brings more complaints and fewer opens.
• Changing ESP. A new ESP means new IPs and often new DNS records. Plan a warm-up.
• New tools sending as you. A CRM, helpdesk or billing system that sends from your domain without SPF and DKIM set up hurts your domain’s reputation. Check your records with the DNS lookup.
• Mistakes. A leaked list, a send to people who complained before, or a colleague who buys a list in good faith can do instant damage.

A monitoring routine

Every day:

• Check Google Postmaster Tools for your spam rate.
• Check bounce and complaint rates for each campaign.
• Check SNDS, Microsoft’s dashboard, for your IP ratings.

Every week:

• Compare engagement trends by provider.
• Check blocklists for new listings.
• Read your DMARC aggregate reports (daily summaries that providers send about email using your domain) for authentication failures.
• Review complaints from feedback loops (services that forward spam reports to you).

Every month:

• Run inbox placement tests: send to test addresses at each provider and see where your email lands. Check authentication first with the Mailwel test inbox.
• Compare how fast your list grows with how fast it shrinks.
• Look for unusual changes in volume or sending patterns.
• Check that you’re removing people who haven’t engaged in a long time.

Recovering from a drop

1. Find the cause. Check complaints, bounces, blocklists, authentication and engagement. Something specific started the drop.
2. Stop the damage. Cut your volume at once. Sending more during a reputation problem makes it worse. If you’re on a blocklist, deal with that.
3. Send only to your most engaged readers, such as people who opened in the last 7–14 days, until your numbers settle.
4. Fix the root cause. Remove the bad list segment, fix the broken DNS record, or change the content that caused complaints.
5. Rebuild slowly. Widen your audience step by step, as in a warm-up.
6. Be patient. Recovery usually takes weeks. Gmail tends to respond faster to good signals. Microsoft can take much longer.
7. Write down what happened, so it doesn’t happen again.

For a step-by-step guide, see Incident: Reputation Tanking Overnight.

Targets to aim for

Number	Good	Excellent
Spam rate (Google Postmaster Tools)	Below 0.1%	Below 0.05%
Gmail compliance status (Postmaster Tools)	All requirements met	All requirements met
SNDS rating (Microsoft)	Green for all IPs	Green, with no trap hits
Bounce rate per campaign	Below 1%	Below 0.5%
Complaint rate (from feedback loops)	Below 0.08%	Below 0.03%
Open rate, leaving out Apple Mail	Above 20%	Above 30%
Blocklist listings	Fewer than one a quarter	None

Any sender who puts list quality ahead of volume can reach these.

The long game

Reputation is never finished. Keep these habits:

• Collect addresses cleanly. Never buy a list.
• Keep engagement high. Stop emailing people who haven’t engaged in a long time, and send each group what it wants.
• Maintain your setup. Check authentication, rotate your DKIM keys, and watch blocklists.
• Keep volume predictable. Ramp up before big campaigns instead of spiking.
• Catch problems early. Daily checks stop small issues from growing.

Providers give trusted senders more slack when something goes wrong. Reputation takes months to build and hours to lose, so protect it.