You spent an hour writing the perfect newsletter. You hit send. And then... nothing. Opens are down. Clicks are flat. Half your subscribers didn't even see it.
The problem isn't your writing. It's deliverability.
Email deliverability is the percentage of emails that actually reach the inbox (not spam, not promotions, not the void). For most newsletter creators, it's an invisible problem — until it isn't.
How inbox providers decide where your email goes
Gmail, Outlook, Yahoo, and Apple Mail all use similar signals to decide whether your email belongs in the inbox, spam folder, or nowhere at all.
The main factors:
1. Sender authentication
This is table stakes. If your emails aren't properly authenticated, many inbox providers will reject them outright.
DKIM — Proves the email hasn't been tampered with in transit. It's a cryptographic signature attached to every email.
SPF — Declares which servers are authorized to send email from your domain.
DMARC — Tells inbox providers what to do when authentication fails (reject, quarantine, or do nothing).
If all three pass, inbox providers know your email is legitimate. If any fail, you're starting with a disadvantage.
2. Sender reputation
Every domain and IP address that sends email has a reputation score. This score is built over time based on:
- Spam complaints — How often recipients mark your emails as spam
- Bounce rate — How many emails bounce (invalid addresses)
- Engagement — Open rates, click rates, replies
- Volume consistency — Sudden spikes in send volume look suspicious
- Spam trap hits — Sending to known spam trap addresses
Your reputation is like a credit score for email. Good behavior over time builds it up. One bad campaign can tank it.
3. Content signals
Inbox providers scan your email content for spam signals:
- Excessive use of ALL CAPS or exclamation marks!!!
- Spammy phrases ("Act now!", "Limited time offer!", "Click here!")
- Image-heavy emails with little text
- Misleading subject lines
- Too many links, especially to low-reputation domains
This doesn't mean you can't use casual language or promotional content. It means you should write like a human, not a marketer from 2005.
4. Recipient engagement
This is increasingly the most important signal. Inbox providers track:
- Does the recipient open your emails?
- Do they click links?
- Do they reply?
- Do they move your email from spam to inbox?
- Do they add you to contacts?
High engagement tells Gmail "this person wants these emails." Low engagement tells Gmail the opposite. Over time, if enough of your subscribers ignore your emails, inbox providers start filtering you out by default.
Common deliverability killers (and how to fix them)
Sending from a shared domain
When you send from @substack.com or @beehiiv.com, your deliverability is tied to every other sender on that platform. If someone else gets flagged, your emails suffer too.
Fix: Send from your own domain. It isolates your reputation from everyone else.
Not cleaning your list
Dead email addresses hurt you in two ways: they increase your bounce rate (which damages reputation), and some dead addresses get recycled as spam traps.
Fix: Remove subscribers who haven't opened a single email in 90 days. Most newsletter platforms offer engagement-based segments for this.
Buying or scraping email lists
This is the fastest way to destroy your sender reputation. Purchased lists are full of spam traps, unengaged contacts, and people who never consented to hear from you.
Fix: Never buy lists. Only send to people who explicitly opted in.
Inconsistent sending patterns
If you normally send 500 emails per week and suddenly blast 10,000, inbox providers treat it as suspicious behavior.
Fix: Grow your sending volume gradually. If you're migrating to a new platform, warm up the new domain by starting with your most engaged subscribers first and gradually increasing volume over 2-4 weeks.
Missing unsubscribe link
Every marketing email is legally required to have a working unsubscribe link (CAN-SPAM, GDPR). If you don't have one, inbox providers penalize you heavily.
Fix: Every reputable newsletter platform adds this automatically. Make sure it's visible and works.
The warm-up process
If you're starting with a brand new domain or IP address, you need to warm it up. Inbox providers are suspicious of new senders — it's a defense against spammers who constantly rotate domains.
Week 1: Send to your 100-200 most engaged subscribers. These are people who always open and click.
Week 2: Expand to your top 500-1000 subscribers.
Week 3: Expand to your top 2000-3000 subscribers.
Week 4: Send to your full list.
During warm-up, monitor your bounce rate, spam complaints, and open rate closely. If anything looks off, slow down and investigate before continuing.
Tools for monitoring deliverability
You don't need to guess whether your emails are reaching the inbox.
Google Postmaster Tools — Free. Shows your domain reputation, spam rate, and authentication status with Gmail specifically.
Mail Tester — Send a test email and get a score with specific recommendations.
Your newsletter platform's analytics — Open rate trends are the most accessible signal. If opens suddenly drop by 20%+, you likely have a deliverability issue.
What good deliverability looks like
For newsletter creators, healthy metrics look like:
| Metric | Healthy Range |
|---|---|
| Open rate | 40-60% (for engaged lists) |
| Bounce rate | Under 2% |
| Spam complaint rate | Under 0.1% |
| Unsubscribe rate | Under 0.5% per send |
If your numbers are significantly below these, investigate authentication first, then list quality, then content.
The deliverability checklist
Before every send, make sure:
- DKIM, SPF, and DMARC are configured and passing
- You're sending from your own domain (not a shared platform domain)
- Your subscriber list is clean (removed bounces and long-term unengaged)
- Unsubscribe link is present and working
- Content doesn't trigger spam filters (no ALL CAPS, excessive exclamation marks)
- Subject line is honest and relevant to the content
The bottom line
Deliverability isn't a one-time setup — it's an ongoing practice. Authenticate your domain, maintain your list, send consistently, and write content people actually want to read.
The best newsletter in the world is worthless if it lands in spam. Take the 30 minutes to get your setup right, and then focus on what matters: the writing.
CocoMail supports guided domain authentication and custom-domain sending, so you can send newsletters from an address on a domain you control. See the features or start sending.