We spent six weeks running 21 deliverability tools against the same sending infrastructure. Three earned a permanent slot in our stack: Mailtrap for pre-send testing, Postmark for transactional reputation, and Smartlead for cold outbound at volume. The other 18 split into two groups — quick diagnostic checkers you use once a quarter, and monitoring platforms that only make sense once you're sending north of 50,000 emails a month.
Here's the thing nobody selling you a deliverability tool will say: most founders don't have a deliverability problem. They have a list problem, a domain-age problem, or a copy problem. A tool will tell you which one. It won't fix it.
Three categories, three jobs, don't buy the wrong one
Every tool we tested falls into one of three buckets. Buying across buckets is fine. Buying the wrong bucket for your stage is how you end up paying $200/month to watch a dashboard tell you your bounce rate is 4%.
Send platforms handle the actual delivery. They own the IP reputation, the DKIM signing, the bounce processing. Mailtrap, Postmark, Smartlead, Instantly, Lemlist, and Resend all live here. You pick one. You don't stack them.
Check tools run a one-off diagnostic. You paste a domain or an email, they tell you if SPF, DKIM, DMARC, and MX are configured correctly, and whether the domain appears on any blocklists. MXToolbox, Mail-Tester, GlockApps, and EasyDMARC's free tier are the ones we kept using. These are free or near-free. Use them before every campaign, not during.
Monitoring tools watch your reputation over time. Google Postmaster Tools, Microsoft SNDS, Validity Everest, and Barracuda Sentinel. These matter once you're sending enough volume that Google and Microsoft have opinions about you. Below 20,000 emails a month, they mostly show you noise.
If you're a solo founder sending 500 cold emails a week, you need one send platform and one free checker. That's it. Everything else is a subscription you'll cancel in month three.
What we actually tested, and how
We set up four sending domains across two providers, warmed them for 21 days, and ran identical campaigns through each tool. Same list, same copy, same send windows. We measured inbox placement using seed lists, tracked bounce handling, and logged how long each tool took to surface a reputation problem.
Some caveats worth stating up front. We tested on a UK-based infrastructure with mostly UK and EU recipients. Results skew differently if you're sending to Gmail-heavy US lists. And we didn't test enterprise contracts — if you're spending $2,000/month on deliverability, you're buying a different product than the one this post covers.
Here's what stood out across the 21:
- Mailtrap — best pre-send testing. Catches HTML issues, spam-trigger phrases, and authentication gaps before you hit send. Free tier is genuinely usable.
- Postmark — cleanest transactional reputation. If you're sending password resets and receipts alongside cold email, keep them on separate infrastructure. Postmark is the one we'd pick for the transactional side.
- Smartlead — best cold outbound platform at volume. Handles mailbox rotation, warmup, and reply detection without you babysitting it. $39/month entry, scales to $94/month for most small teams.
- MXToolbox — the free checker we still open weekly. Ugly interface, accurate results, no upsell pressure.
- Google Postmaster Tools — free, and the only source of truth for how Gmail actually sees you. Set it up even if you're sending 1,000 emails a month.
The tools we dropped: three "AI deliverability optimisers" that promised to rewrite subject lines for inbox placement. They didn't move placement in our tests. Two monitoring platforms that cost $99/month and surfaced the same data as Postmaster Tools. And one checker that flagged our correctly-configured DMARC as broken — twice.
Authentication is not a tool problem
Half the deliverability tools on the market exist because founders haven't set up SPF, DKIM, and DMARC properly. That's not a tooling gap. That's a DNS gap.
If your DMARC record is still at p=none, no tool will save your inbox placement. Google and Microsoft closed that loophole in 2024 and have been tightening enforcement since. We wrote about why your p=none config is now a spam filter — read that before you buy anything else.
The same applies to list hygiene. A tool can tell you 12% of your list is invalid. It can't tell you that you scraped those addresses from a conference attendee PDF without consent. That's a compliance problem, and it's getting more expensive. We covered the state-by-state cold email compliance picture if you're sending into the US.
Where tools genuinely help: catching configuration drift. Domains break. DKIM keys rotate. Someone on your team edits a DNS record and forgets to update the selector. A weekly check with MXToolbox or EasyDMARC catches that in 30 seconds. That's the real value of the check-tool category.
What we'd actually recommend by stage
Solo founder, under 1,000 emails a month. One send platform (Smartlead or Instantly), MXToolbox for weekly checks, Google Postmaster Tools set up and ignored until you cross 5,000/month. Total cost: $39–$49/month.
Two-to-five person sales team, 5,000–50,000 emails a month. Add a proper monitoring tool. Validity Everest if you have budget, EasyDMARC's paid tier if you don't. Keep transactional and cold email on separate domains. Total cost: $150–$400/month.
Above 50,000 emails a month. You're now in territory where a dedicated deliverability consultant costs less than the revenue you lose from a 10% placement drop. Tools alone won't cut it. Budget for both.
What we'd skip at every stage: AI subject line optimisers, "inbox placement guarantee" services, and anything that charges monthly for a check you can run free elsewhere. The category is crowded with products solving problems that authentication and list hygiene already solved.
If you want to try this
Start with the free stuff. Set up Google Postmaster Tools, run your domain through MXToolbox, and check your DMARC record. If those three come back clean and you're still landing in spam, then you have a tooling decision to make.
If the bottleneck is the outbound workflow itself — finding prospects, scoring inboxes, drafting emails that don't read like a template — give MiraReach a try. We handle the sending infrastructure and the personalisation. You still press send.
— Mira