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Brew is the AI-native ESP. Define your brand once, ship on-brand email in minutes.
Master email deliverability with this comprehensive guide. Learn what affects inbox placement and how to fix common deliverability problems.
Email deliverability is the foundation of email marketing. If your emails don't reach the inbox, nothing else matters—your brilliant copy, beautiful design, and perfect timing are all wasted.
This guide explains what affects deliverability, how to diagnose problems, and how to fix them.
Deliverability measures whether your emails reach subscribers' inboxes versus spam folders or being blocked entirely.
Critical distinction:
You can have 99% delivery rate but terrible inbox placement. The emails "delivered" might all be in spam.
Your sender reputation is like a credit score for email. Mailbox providers track:
| Factor | Impact |
|---|---|
| Spam complaints | High negative |
| Bounce rates | High negative |
| Engagement (opens, clicks) | High positive |
| Spam trap hits | Severe negative |
| Sending patterns | Medium |
| List quality | High |
Reputation is built over time and can take weeks to recover if damaged.
Three protocols verify you're a legitimate sender:
SPF (Sender Policy Framework):
DKIM (DomainKeys Identified Mail):
DMARC (Domain-based Message Authentication):
p=none policy is the accepted floor. A missing DMARC record draws Gmail error 4.7.31.Spam filters analyze your email content:
| Factor | Watch Out For |
|---|---|
| Spam trigger words | "Free," "act now," excessive claims |
| Image-to-text ratio | Too many images, too little text |
| Link quality | Shortened URLs, suspicious domains |
| HTML quality | Broken code, hidden text |
| Subject line | ALL CAPS, excessive punctuation |
Your list directly impacts reputation:
| Metric | Target | Problem Zone |
|---|---|---|
| Bounce rate | <2% | >5% |
| Spam complaints | <0.1% | >0.3% |
| Engagement rate | >15% | <5% |
| List age | Fresh | Years old |
Since February 1, 2024, Google and Yahoo enforce a shared set of requirements. They apply to all senders, with stricter rules for bulk senders — anyone sending close to 5,000 messages or more per day to personal Gmail accounts (counted across your whole primary domain, including subdomains; the status never expires once you cross it).
All senders must:
Message-ID and a single From: address that honestly identifies the sender (no deceptive Re:/Fwd: or emoji-as-graphics)Bulk senders (~5,000+/day) must additionally:
p=none is an acceptable floor)From: domain with the SPF or DKIM domainMarketing and subscribed messages must include one-click unsubscribe headers so recipients can opt out from within Gmail/Yahoo in a single click:
List-Unsubscribe: <https://yourdomain.com/unsubscribe/...>
List-Unsubscribe-Post: List-Unsubscribe=One-Click
mailto:-only or plain-link unsubscribe does not satisfy the requirement.Through 2024–2025 non-compliant mail was mostly deferred with temporary 4xx errors. As of November 2025, Google escalated to permanent 5xx (550) rejections — non-compliant messages are refused outright and not retried. Enhanced status codes tell you what failed: 5.7.25 (PTR), 5.7.27 (SPF), 5.7.29 (TLS), 5.7.30 (DKIM), 4.7.31 (missing DMARC), 4.7.32 (From misalignment), and 4.7.28 (rate limited — stop sending for at least 10 minutes).
On Brew: authentication, TLS, PTR, one-click unsubscribe headers, and body-link enforcement are handled for you on every marketing send. Publish your DNS records (including DMARC), keep your list clean, and watch your spam rate.
🚩 Open rates declining across all segments 🚩 Bounce rate consistently above 2% 🚩 Spam complaints above 0.1% 🚩 Test emails landing in spam 🚩 Sudden engagement drops 🚩 Subscribers saying they didn't receive emails
Google Postmaster Tools:
Microsoft SNDS:
MXToolbox:
Mail Tester:
Run these checks:
5.7.25 when missing.)5.7.29 when absent.)On a managed platform like Brew, SPF and DKIM are generated for you, TLS and PTR are handled by the sending infrastructure, and DMARC is provided as a record to add. Your job is to publish the records and keep your spam rate low.
SPF Setup:
v=spf1 include:youresp.com ~all
Replace with your email platform's SPF include.
DKIM Setup: Follow your email platform's instructions to add the DKIM record.
DMARC Setup: Start with monitoring:
v=DMARC1; p=none; rua=mailto:dmarc@yourdomain.com
Progress to enforcement over time:
v=DMARC1; p=quarantine; rua=mailto:dmarc@yourdomain.com
Remove:
Higher engagement = better reputation:
If starting fresh or recovering:
| Week | Daily Volume | Target |
|---|---|---|
| 1 | 100-500 | Most engaged only |
| 2 | 500-1,000 | Engaged subscribers |
| 3 | 1,000-5,000 | Broader engaged |
| 4 | 5,000-10,000 | Most active |
| 5+ | Normal volume | Full list (engaged) |
Monitor reputation closely throughout.
✅ Double opt-in for best quality ✅ Clear expectations at signup ✅ Immediate welcome email ✅ Regular list hygiene
❌ Never buy lists ❌ Don't add people without consent ❌ Avoid aggressive scraped contacts ❌ Don't use old, cold lists
✅ Consistent sending schedule ✅ Segment for relevance ✅ Honor unsubscribes immediately ✅ Monitor engagement metrics ✅ Regular list cleaning
❌ Don't send to cold lists suddenly ❌ Avoid erratic volume spikes ❌ Never ignore bounce handling ❌ Don't send to entire list always
✅ Clean, valid HTML ✅ Plain text version included ✅ Balanced text-to-image ratio ✅ Valid, reputable links ✅ Clear sender identity
❌ Don't use excessive link shorteners ❌ Avoid spam trigger words in excess ❌ Don't hide text (tiny fonts, white on white) ❌ Never mislead with subject lines
| Severity | Recovery Time |
|---|---|
| Minor (temporary dip) | 1-2 weeks |
| Moderate (reputation damage) | 4-6 weeks |
| Severe (blacklisted) | 2-3 months or new domain |
Different platforms have different deliverability characteristics:
Shared IP platforms (most small business tools):
Dedicated IP (enterprise/high volume):
Brew handles deliverability infrastructure for you, with best practices built into the platform.
Deliverability isn't glamorous, but it's essential. The best email in the world is worthless if it never reaches the inbox.
Focus on:
Ready to send emails that actually arrive? Try Brew for email marketing with deliverability best practices built in.
For the legal split, read transactional emails. For opens after Apple prefetch, read email metrics that matter. To contact us about this article, write Brew support.
Email deliverability is whether the message reaches the inbox, not whether the ESP says sent.
Authentication is SPF, DKIM, and DMARC on the domain you send from.
A complaint rate is the share of recipients who mark the mail as spam.
For example, a bought list can look large in the ESP and still fail Gmail's spam-rate ceiling.
| Move | Why it matters |
|---|---|
| Authenticate first | Volume without SPF, DKIM, and DMARC is a fast way to the spam folder |
| Clean quiet names | Dead addresses teach mailbox providers the wrong lesson |
US commercial mail still follows the FTC CAN-SPAM guide and 16 CFR 316.3. Bulk sending still has to meet Gmail's sender requirements. To contact us about this article, use the support link above.
Deliverability is whether your mail reaches the inbox instead of spam or a block. A high delivery rate can still mean most accepted mail landed in junk.
Gmail's sender requirements apply at 5,000 or more recipients a day to personal Gmail. Authenticate with SPF, DKIM, and DMARC. Put one-click unsubscribe on marketing mail. Stay under a 0.1% spam rate.
Yahoo tells high-volume senders to split them. A cart campaign that shares an IP with password resets puts receipts in the same reputation bucket as the campaign.
RFC 8058. You need List-Unsubscribe plus List-Unsubscribe-Post: List-Unsubscribe=One-Click. A footer link that dumps someone on a preferences page is not enough.
