Email deliverability - explained plainly
Practical guides on inbox placement, warmup, blacklist monitoring, and sender reputation — written for sales teams, founders, and developers who need their email to land in the inbox, not the spam folder.
Email deliverability determines whether your emails reach the inbox or land in spam — and why. These guides cover the complete stack: warming a new sending domain to build sender reputation, running inbox placement tests to verify where mail actually lands across Gmail, Outlook, and Yahoo, monitoring blacklists to catch reputation problems before they compound, and repairing sender reputation when deliverability has already degraded. Written for sales teams sending cold outreach from dedicated domains, founders configuring transactional email, and developers building email infrastructure that needs to reliably reach the inbox.
Warmup
How to warm up a new email domain
A new domain has zero sending history. Before cold outreach can run at volume, you need 30 days of warmup. The right schedule, what to set up first, and the four mistakes that cause warmup to fail.
WarmupDoes email warmup actually work?
Yes — when the seed network is made of real inboxes. Here is why network quality matters more than network size, and the question your current warmup tool probably cannot answer.
WarmupEmail warmup for cold outreach
Cold outreach from a new domain without warmup goes straight to spam. The right ramp schedule, the four mistakes that cause warmup to fail, and what to look for in a platform.
WarmupWhy your warmup score says 92 — and your campaign is still in spam
The score was accurate. The problem is what it was measuring against. How synthetic seed networks produce inflated scores, and what a real seed mailbox needs to provide a genuine trust signal.
WarmupCan a warm-up tool get your domain blocked?
Four mechanisms that cause warm-up tools to harm the domain they are meant to protect: shared credential pools, excess inbox access, undisclosed network composition, and undifferentiated signup pools. What to check before you connect.
Testing & monitoring
Email deliverability tools — what to use and when
Four categories of tools: inbox placement tests, authentication checkers, blacklist monitors, and warmup. What each does, when to reach for it, and a symptom-to-tool guide for common deliverability problems.
Testing & monitoringHow to test whether your emails land in the inbox or spam
An inbox placement test sends a real message to seed mailboxes and reports exactly where it arrived — per provider. Why open rates alone cannot tell you this, and what a full test checks.
Testing & monitoringHow to monitor if your sending domain is on an email blacklist
A blacklist listing can block delivery silently within hours of a spam complaint. The major lists that affect real delivery at scale, how to get delisted, and why continuous monitoring beats one-time checks.
Testing & monitoringAI email deliverability software — what it does and how to evaluate it
AI improves open rates by improving inbox placement. What placement prediction, spam scoring, reputation trend analysis, and anomaly detection actually do — and what AI cannot fix.
AI & Deliverability
Does AI-written cold email go to spam?
ISPs don't scan for AI authorship — but 51% of spam is now AI-generated, and filters are learning the patterns. The honest answer on risk, and what actually determines where your email lands.
AI & DeliverabilityHow ISPs detect AI-generated email
No ISP runs a dedicated AI scanner on your content. Detection is indirect: reputation-based, engagement-based, and pattern-based. Here's how the two pathways work and what you can do about them.
AI & DeliverabilityAI cold email and sender reputation
AI outreach tools reduce friction on volume. Volume with imprecise targeting produces the engagement signal degradation that moves domains toward spam. The mechanism, symptoms, and recovery path.
AI & DeliverabilityClay and Instantly deliverability guide
Clay and Instantly don't manage your sender reputation. Here's the checklist every team using these tools needs before scaling — authentication, warmup, placement testing, and domain strategy.
Fixing problems
Why are my emails going to spam? Causes, diagnosis and fixes
Six ordered steps: diagnose first with a placement test, fix authentication, check blacklists, clean your list, reduce complaint rates, and warm up if volume increased. Why the order matters and what not to do first.
Fixing problemsHow to improve email sender reputation
What sender reputation is, what damages it, how to check it across providers, and six proactive steps to improve it — whether building on a new domain, maintaining a healthy one, or recovering.
Fixing problemsHow to fix your email sender reputation
A six-step ordered guide: diagnose before you act, pause and clean your list, fix authentication, get off blacklists, rebuild with controlled volume, then monitor. What ISPs actually measure and why the order matters.
By use case
Alternatives & comparisons
Warmy alternative
Warmy has the largest G2 review moat in the category. The two most common complaints: per-inbox pricing ($400–500/mo at 10+ inboxes) and silent disconnections (~42 G2 mentions). How InboxPlease compares across pricing, network transparency, and M365 support.
Alternatives & comparisonsLemwarm alternative
Free for Lemlist Email Pro+ subscribers. Concerns: almost no standalone review presence, disputed Smart Cluster matching, and a network reviewers describe as lacking transparency. The wedge is knowing exactly who is warming you.
Alternatives & comparisonsFolderly alternative
Strong support (9.8/10 G2 score), Belkins-backed. Four concerns documented by reviewers: a 42,000-email weekend blowout from a bug, mandatory annual contracts, placement testing as a separate add-on, and inbox access required for audits.
Alternatives & comparisonsMailReach alternative
The best-supported tool in the category — 4.9 cross-platform, no G2/Trustpilot gap. The comparison is about scope: no free trial, no free placement test, 35-seed panel, no blacklist monitoring or DMARC analytics.
Alternatives & comparisonsSaleshandy alternative
A mature cold email platform with sequences, inbox rotation, LinkedIn outreach, and bundled warm-up. If you only need deliverability, you're paying for an outreach stack you won't use — and getting a tool whose roadmap isn't built around your problem.
Alternatives & comparisonsSnov.io alternative
Prospecting and sales automation platform — email finder, data enrichment, drip sequences, and bundled warm-up. The comparison is about scope: if deliverability is the goal, Snov.io is a full sales stack that includes warm-up as one feature.
Alternatives & comparisonsSalesforge alternative
AI cold email platform built for multi-sender outreach at scale. Warmup is bundled via Primebox. The wedge: no blacklist monitoring, no DMARC analytics, no free placement test, and full inbox access required for outreach features.
Alternatives & comparisonsWarmforge alternative
AI-generated warmup conversations with a genuine free tier. A focused warmup tool — no inbox placement testing, no blacklist monitoring, no DMARC analytics, and full inbox access required vs. InboxPlease's send-only OAuth model.
Alternatives & comparisonsTrulyInbox alternative
Dedicated warmup and placement tool, not a bundled outreach feature. The comparison is about credential scope: TrulyInbox requires full inbox access for the engagement loop; InboxPlease uses send-only OAuth and never reads your inbox.
Alternatives & comparisonsInstantly alternative
Multi-mailbox cold email platform with sequences, inbox rotation, A/B testing, and bundled warm-up via Warmly. If deliverability is the goal, you're paying for sequencing infrastructure you won't use — with no blacklist monitoring or free placement test.
From the blog
We never read your inbox
Why most warm-up tools require full inbox access, how InboxPlease uses send-only OAuth instead, and the verbatim Terms of Service language under Google and Microsoft data-use commitments that makes this a structural constraint, not a marketing claim.
From the blogWhy every warm-up tool's G2 score is 4.8 and its Trustpilot score isn't
G2 captures users who reached proficiency. Trustpilot captures users who hit friction. The gap between them is a more predictive signal for the first 90 days than either score alone — and it exists for several major tools in this category.
Not sure where to start? The free test checks your inbox placement, authentication, and blacklist status in 60 seconds — and tells you exactly what to fix.
Run free testTest your deliverability now
Inbox placement across Gmail, Outlook, and Yahoo. SPF, DKIM, and DMARC on a real delivered message. Blacklist status. 60 seconds, no account required.