The fastest way to land in the primary inbox is to combine three jobs: domain authentication, ongoing warm-up, and active placement monitoring. Most deliverability tools do one or two of those well. We tested the seven most-recommended platforms in 2026 plus the all-in-one approach we use ourselves at ACA. This guide ranks each by what it actually does well, where it falls short, and what it costs, so you can build a stack that fits your sending volume and budget.
Short answer: If you send cold email at scale and want one platform that handles warm-up, inbox rotation, monitoring, and sending in a single sequence, use ACA. If you already run a sender like Instantly, Smartlead, or Lemlist and just need to patch a deliverability gap, pair it with MailReach for warm-up, GlockApps for placement tests, and MXToolbox for blacklist alerts. Warmbox is the cheap option for solo founders. Folderly is for enterprise teams with a real budget. Google Postmaster Tools is free and non-negotiable if you send to Gmail.
What Email Deliverability Tools Actually Do
"Deliverability tool" is a broad label that covers four distinct jobs. Knowing which job you need is the difference between fixing a real problem and paying for a feature you will never use.
- Warm-up services: simulate organic engagement on your inbox by sending and receiving emails inside a pool of other accounts. The goal is to build sender reputation gradually before you start outreach, then maintain it during active sending.
- Inbox placement testing: send seed emails to a panel of test accounts at Gmail, Outlook, Yahoo, and corporate domains, then report where each landed (inbox, promotions, spam, blocked).
- Reputation and blacklist monitoring: watch your IP and domain against the major blacklists and alert you when something changes.
- Mailbox-level signals: reports straight from the provider (Google Postmaster, Microsoft SNDS) on spam rate, domain reputation, and authentication results.
Most teams need at least two of these. Pure warm-up without monitoring is flying blind. Monitoring without warm-up is watching the wreck happen. The right stack covers all four functions, ideally without paying four separate vendors.
ACA: The All-in-One Outreach and Deliverability Platform
ACA combines sending, multi-channel sequencing, AI content, and deliverability infrastructure in one platform. For deliverability specifically, ACA handles warm-up on every connected inbox, rotates sends across multiple accounts inside a single sequence, and monitors per-inbox performance so you can pull a struggling mailbox out before it drags the rest down.
Pricing: BYOK (Bring Your Own Key) model, $50 to $80 per month for the platform. No per-seat fees. All channels and warm-up included.
What it does well:
- Native warm-up runs continuously on every connected mailbox, no separate subscription
- Inbox rotation distributes volume across 2 to 20 mailboxes inside one campaign automatically
- Per-inbox health metrics flag reputation drops before they hit your reply rates
- Multi-channel fallback (LinkedIn, WhatsApp, Instagram) reduces email volume per prospect, which protects sender reputation over time
- Unified inbox keeps reply tracking and engagement clean across all sending accounts
What it misses: No standalone seed-list placement testing like GlockApps. No deep blacklist scanning across hundreds of RBLs like MXToolbox. For high-volume senders who want a dedicated deliverability audit on top, you still pair ACA with a placement tester.
Best for: Agencies and founders who want one platform for outreach, content, and deliverability instead of stitching together five separate tools.
MailReach: The Warm-Up Specialist
MailReach is a focused warm-up service with one of the larger sender pools on the market. It connects to any SMTP-capable inbox (Google Workspace, Microsoft 365, custom domains) and runs simulated engagement in the background.
Pricing: Around $25 per month per inbox for the Starter plan. Volume discounts above 5 inboxes.
What it does well:
- Real-mailbox warm-up pool of tens of thousands of accounts across major providers
- Detailed warm-up reports show spam vs inbox placement of your warm-up emails over time
- Spam test feature lets you send a single email to MailReach's seed list and see exact placement at Gmail, Outlook, Yahoo
- Clean dashboard, easy to connect new inboxes
What it misses: Warm-up only. No sending platform, no campaign builder, no CRM. You pay separately for the tool that actually sends your outreach. At 10 inboxes you are looking at $250 per month just for warm-up, before you add a sender like Smartlead or Instantly.
Best for: Teams already committed to a separate sending platform that needs a high-quality warm-up bolt-on.
Lemwarm: Warm-Up Plus Deliverability Hub
Lemwarm is Lemlist's deliverability product. You can buy it standalone or get it included with any Lemlist plan. It combines warm-up with a deliverability hub that tracks domain authentication, reputation, and DNS health.
Pricing: Standalone around $29 per month per inbox. Included free with all Lemlist plans (Email Pro starts at 63 EUR per user per month annual).
What it does well:
- Continuous warm-up with engagement curve adjustment based on inbox age
- Deliverability hub flags missing or broken SPF, DKIM, DMARC records
- Domain purchase and DNS auto-setup if you are spinning up new secondary domains
- Good integration story if you already use Lemlist for sending
What it misses: Standalone Lemwarm is competitively priced, but the real value unlocks when bundled with Lemlist. If you do not want Lemlist's sender, you are better off with MailReach at a similar price point.
Best for: Lemlist users (gets a lot of value as a bundled feature). Marginal as a standalone purchase.
Warmbox: The Budget Warm-Up Option
Warmbox is the cheap, no-frills warm-up service. Smaller mailbox pool than MailReach or Lemwarm, but the price reflects it.
Pricing: Starts around $15 per month per inbox on annual billing. Multi-inbox plans bring the per-mailbox cost down further.
What it does well:
- Lowest price per inbox among the well-known warm-up services
- Simple setup: connect inbox, choose ramp curve, done
- Decent reporting on warm-up performance
- Works fine for low-volume sending (under 30 emails per inbox per day)
What it misses: Smaller and less diverse mailbox pool means the warm-up signal looks more uniform to modern filters. No advanced features like content rotation, custom warm-up templates, or per-provider engagement balancing. If you are sending serious volume, you outgrow it quickly.
Best for: Solo founders and freelancers running 1 to 3 inboxes at low volume on a tight budget.
Folderly: Enterprise Deliverability Fix
Folderly is positioned as the premium, hands-on deliverability solution. It includes warm-up, monitoring, content analysis, and a dedicated team that audits your setup and recommends fixes.
Pricing: Around $120 per month per mailbox on the standard plan. Enterprise plans run higher with custom pricing.
What it does well:
- Deep deliverability audit across authentication, DNS, content, and sending patterns
- Content analyzer scans your actual outreach copy for spam triggers and suggests rewrites
- Dedicated specialist on higher tiers who reviews your setup and tells you exactly what to fix
- Strong reporting with placement tests, sender score, and historical reputation graphs
What it misses: Price. At $120 per mailbox per month, a 10-inbox setup runs $1,200 per month for deliverability alone. That is more than most sending platforms cost. Overkill for SMBs running standard cold outreach. The value is real for enterprise teams where one blacklisting event would cost more than a year of Folderly fees, but for everyone else the math does not work.
Best for: Enterprise sales teams, regulated industries, or organizations where the cost of a single deliverability failure exceeds the annual tool cost.
GlockApps: Inbox Placement Testing
GlockApps does one thing extremely well: it tells you exactly where your emails land at the major providers. Send a test email to their seed list, get back a report showing inbox, promotions, spam, or missing for Gmail, Outlook, Yahoo, AOL, and corporate domains.
Pricing: Free trial. Paid plans start around $59 per month for 50 spam tests. Higher tiers include uptime monitoring, DMARC analysis, and Postmaster integration.
What it does well:
- The most detailed inbox placement reports in the category: per-provider, per-region breakdowns
- Identifies which authentication records passed or failed for each receiving server
- Content analysis shows which spam triggers fired
- DMARC analyzer aggregates reports from your domain into a readable dashboard
- Bounce monitoring tracks delivery failures over time
What it misses: No warm-up. No sending. Pure measurement. You need to pair GlockApps with a warm-up service and a sender to have a complete stack.
Best for: Teams that already have warm-up and sending sorted but need real visibility into where their emails are actually landing.
Why placement testing matters: Open rates have been unreliable since Apple Mail Privacy Protection started inflating them in 2021. A 60% open rate can mask a 30% spam folder rate. Direct seed-list testing is the only way to know your true inbox placement. In our experience, running a placement test before every new campaign and after any change to sending infrastructure catches deliverability drift weeks before it tanks a campaign.
MXToolbox: Blacklist and DNS Monitoring
MXToolbox is the industry-standard utility for DNS lookups, blacklist checks, and email authentication validation. Most of its core features are free; paid plans add ongoing monitoring and alerts.
Pricing: Free for one-off lookups. MXToolbox Delivery Center starts around $129 per month for active monitoring. Higher tiers add more domains and historical data.
What it does well:
- Checks your IP and domain against 100+ blacklists in seconds
- Validates SPF, DKIM, DMARC records and flags configuration errors
- SMTP diagnostic shows how a remote mail server sees your sending setup
- Continuous monitoring on paid plans alerts you the moment a blacklist hits
- Free tier covers most ad-hoc deliverability investigations
What it misses: No warm-up. No placement testing (it does not tell you whether you land in inbox or spam, only whether you can technically deliver). Paid plans get expensive at scale if you monitor many domains.
Best for: Every cold email operator should have the free MXToolbox bookmarked. Paid plans are worth it for agencies managing 5+ sending domains where one blacklisting event would cost real money.
Google Postmaster Tools: Free Gmail Reputation Data
Google Postmaster Tools is Google's official deliverability dashboard for senders. It is free. It shows you exactly what Gmail thinks of your domain.
Pricing: Free.
What it does well:
- Domain and IP reputation scores (High, Medium, Low, Bad) for your sending infrastructure
- Spam complaint rate, the single most important deliverability metric for Gmail
- Authentication pass rates for SPF, DKIM, DMARC
- Delivery errors broken down by failure type
- Direct from Gmail, which receives the majority of B2B email, no proxy or estimate
What it misses: Requires a minimum daily volume to Gmail addresses (a few hundred per day) before data appears. Gmail only, no data on Outlook, Yahoo, or other providers. No warm-up, no testing, no alerting (you check the dashboard manually).
Best for: Anyone sending more than 100 emails per day to Gmail addresses. Set it up on day one, check it weekly. There is no excuse to skip a free tool that tells you what the largest mailbox provider thinks of you.
Side-by-Side Comparison
| Tool | Warm-up | Placement test | Blacklist monitor | Sending | Starting price |
|---|---|---|---|---|---|
| ACA | Yes | Basic | No | Yes (multi-channel) | $50/mo BYOK |
| MailReach | Yes | Basic | No | No | $25/mo per inbox |
| Lemwarm | Yes | No | No | No (standalone) | $29/mo per inbox |
| Warmbox | Yes | No | No | No | $15/mo per inbox |
| Folderly | Yes | Yes | Yes | No | $120/mo per inbox |
| GlockApps | No | Yes | Partial | No | $59/mo |
| MXToolbox | No | No | Yes | No | Free / $129/mo |
| Postmaster Tools | No | No | No | No | Free |
How to Pick the Right Stack
Use ACA when: you want one platform for sending, warm-up, monitoring, and multi-channel outreach. Flat pricing regardless of team size or inbox count.
Use MailReach when: you already run Smartlead or Instantly for sending and just need a high-quality warm-up bolt-on.
Use Warmbox when: you are a solo founder running 1 to 3 inboxes at low volume and price is the main constraint.
Use Folderly when: you are enterprise, regulated, or running a high-stakes campaign where one blacklist event would cost more than a year of fees.
Use GlockApps when: your sending and warm-up are sorted, and you need real inbox placement data to optimize.
Use MXToolbox when: you manage multiple sending domains and need continuous blacklist alerts. The free tier alone is mandatory.
Use Postmaster Tools when: you send to Gmail. Always. It is free.
The biggest mistake we see is stacking tools that overlap and ignoring the layer that matters. Three warm-up services do not warm three times faster. They just cost three times as much. Build the stack by function: one warm-up provider, one placement tester, one monitoring layer, and a sender that respects deliverability fundamentals.
For most agencies, the ACA approach (sending plus warm-up plus multi-channel in one platform) combined with GlockApps for placement spot-checks and the free MXToolbox plus Postmaster Tools for monitoring covers every function for under $150 per month total. That is less than a single Folderly inbox and considerably less than paying MailReach plus Smartlead plus a CRM plus a content tool separately.
Frequently Asked Questions
Do I really need a separate warm-up tool?
Yes, unless your sending platform includes warm-up natively (ACA does, Lemlist does via Lemwarm). Cold email without warm-up on a new inbox gets flagged within days. Existing inboxes also benefit from ongoing warm-up between campaigns to maintain reputation.
How long does email warm-up take?
Three to four weeks minimum for a brand new inbox before you start real outreach. Six weeks is safer. Keep warm-up running in the background even after you go live. The simulated engagement maintains baseline reputation during active campaigns.
Can I just use Google Postmaster Tools and skip the paid options?
If you only send to Gmail and only need reputation visibility, yes. But Postmaster Tools requires minimum volume to populate data, only covers Gmail, and does not include warm-up or testing. For most B2B cold email it is one piece of the stack, not the whole thing.
What is the cheapest viable deliverability stack?
Warmbox at around $15 per inbox for warm-up, GlockApps trial or pay-per-test for occasional placement checks, free MXToolbox for blacklist lookups, and free Postmaster Tools for Gmail reputation. Total: under $30 per month per inbox for the basics. Works for solo operators with 1 to 3 inboxes.
How often should I run an inbox placement test?
Before every new campaign, after any change to sending infrastructure (new domain, new DNS records, new sender), and at least monthly during active outreach. Placement drift is gradual. You want to catch it within weeks, not after a campaign tanks.
Will deliverability tools fix bad cold email copy?
No. Tools fix infrastructure problems. They do not fix offers that nobody wants, lists that are dirty, or copy that triggers spam complaints. If your spam complaint rate is high in Postmaster Tools, the problem is upstream of any tool in this list. It is your targeting and your message.