What Email Deliverability Tools Can and Cannot Tell You

Email deliverability tools measure your sending side and nothing else: authentication, domain and IP reputation, spam rate, blocklist status, placement against seed mailboxes. Not one of them can tell you whether the store you are about to email had any reason to hear from you this week. That is usually the half of the problem that is actually broken.

The disclosure first. We build Keaz Signals, which sells buying signals for ecommerce outreach. We do not sell a deliverability tool, mailboxes, domains, warmup or an SMTP service, and we will not end this article by suggesting you buy one from us. Our sending runs through Instantly, in the customer's own workspace, on their own domains. That is the whole conflict, and it is why we can describe this category without needing you to pick a winner from it.

The category does four separable jobs, and most product pages blur them into one promise. Separating them is the whole of the buying decision:

• Authentication checkers read your DNS: is there an SPF record, a DKIM key, a DMARC policy, a valid reverse lookup.
• Reputation monitors report what a receiving provider says about your domain and IP over time.
• Blocklist monitors watch public lists and tell you when your sending IP turns up on one.
• Placement testers send to a panel of seed mailboxes the vendor controls, and report where the message landed in those mailboxes.

Only the first is a plain fact about your configuration, and it is the one you can verify for free. The other three are observations, and every observation has a scope. The scope is where the category gets misread.

Google publishes its requirements, so a tool that charges you to discover them is selling convenience rather than knowledge. Retrieved 11 September 2026, the Gmail sender guidelines state that since 1 February 2024 every sender to Gmail accounts must set up SPF or DKIM, publish valid forward and reverse DNS records, transmit over TLS, format messages to RFC 5322, and keep spam rates reported in Postmaster Tools below 0.3%.

Above 5,000 messages a day to Gmail accounts the same page adds SPF and DKIM and DMARC together, alignment between the From: domain and the authenticating domain, and one-click unsubscribe on marketing and subscribed messages.

The monitoring section is stricter than the requirement:

Keep spam rates reported in Postmaster Tools below 0.10% and avoid ever reaching a spam rate of 0.30% or higher.

An authentication checker tells you whether you meet the first list. It tells you nothing about the second, because the second is a running score set by the people receiving your mail.

Google Postmaster Tools is free, it is the source every deliverability dashboard quotes, and for B2B outreach it is partly blind. Its own setup page states the limit plainly, retrieved 11 September 2026:

Data in Postmaster Tools only applies to messages sent to personal Gmail accounts. A personal Gmail account is an account that ends in @gmail.com or @googlemail.com.

If you sell to ecommerce stores, a large share of the addresses you write to are on the store's own domain. Those sends produce no Postmaster row at all. You are reading a dashboard about the consumer slice of your list and inferring the rest.

The second limit catches small senders. The same page says data may be missing if the total number of messages for a given day is too low, to protect users' privacy. An agency sending a few hundred messages a day can have every record correct and still open an empty dashboard — which reads, wrongly, like a problem to fix with a purchase.

That is a scope limit in a free tool, not a case against it. It is the reason a paid placement tester exists at all, and the reason its seed panel is worth asking about before you buy.

No tool, no sending provider and no agency can arrange preferential treatment at Gmail. Google says so on the same page as the requirements, retrieved 11 September 2026:

Google and Gmail don't accept allowlist requests from email providers. We can't guarantee messages sent by email providers will pass Gmail's spam filters.

Read that next to how reputation is counted. Google states it tracks volume, feedback and limits per domain and per IP address, that SPF and DKIM quotas are specific to your domain, and that the IP address quota is shared for all senders using that IP — so when a shared IP hits its quota, every domain on it stops sending.

So a monitoring tool can tell you that a shared IP went bad. It cannot make it good, and neither can the vendor who sold you the seat on it. That is a structural difference, not a claim about anyone's compliance. The same structure explains why adding mailboxes on one domain adds quota while sharing a single reputation, which we worked through in Gmail Multiple Inboxes Is Not Sending Capacity.

We are not going to rank the deliverability tools we run, publish an inbox-placement percentage, or tell you which one is worth its price. We did not run a controlled comparison — same list, same copy, same domains, same week — and without that, any ranking we published would be a preference dressed as a measurement.

This is worth saying out loud because the round-ups that do carry those numbers rarely say where they came from. A placement figure is only meaningful with the seed panel, the sending domains, the volume and the date attached to it. Strip those away and it is a number that travels well and means nothing.

We will not compare prices across these tools either. What each one meters is not the same thing — domains, mailboxes, seed sends, monitored IPs — and a table that pretends otherwise would be dishonest.

One number is worth planning against, and it is Google's rather than ours: a Postmaster Tools spam rate below 0.10%. It is published, it is measurable on your own domain, and it is the threshold Google itself asks you to hold. Also from Google, for anyone building a dashboard around opens: Google doesn't track open rates, and cannot verify open rates reported by third parties.

Every deliverability tool watches the sending end. None of them looks at the list, and Google's own guidelines put the list first. Two lines from the sender guidelines, quoted as published and retrieved 11 September 2026:

Don't purchase email addresses from other companies.

Don't send messages to people who didn't sign up to get messages from you. These recipients might mark your messages as spam, and future messages to these recipients will be marked as spam.

Spam rate is the metric the whole category orbits, and spam rate is produced by recipients. Fix authentication and you stop being rejected; you do not stop being reported. That part is decided by who is on the list and whether the message had a reason to arrive — which is why more throughput makes a badly timed campaign worse, an argument we set out in A Bulk Email Sender Solves Throughput, Not Timing.

If your authentication is wrong, your IP is listed, or you have no idea what your spam rate is, buy the deliverability tool. That is a real problem with a real product category attached to it, and nothing on this site fixes it. We provide no mailboxes, no domains, no warmup and no reputation monitoring, and we have no plans to.

The rest of where we lose, plainly. We do not export — leads move into campaigns and stay there, which for some teams is a dealbreaker and should be. There are no LinkedIn signals and no LinkedIn sending, and none are planned. We watch Shopify and WooCommerce stores in Europe and North America, and nothing else. We are GDPR-conscious by design and will not claim more than that; responsibility for what you send stays with you.

What we change is the list and its timing. As of September 2026 we watch 4.1 million Shopify and WooCommerce stores, re-scraped weekly, and roughly 41,200 of them carried a fresh signal in the last seven days. Those are our own moving numbers and they move. The buying signal catalogue lists what we watch for, and the ecommerce leads database is where those stores arrive with contacts attached. Signups start with 1,000 free leads.

• Email sender guidelines, Gmail Help, retrieved 11 September 2026
• Set up Postmaster Tools, Gmail Help, retrieved 11 September 2026
• Keaz Signals store coverage and weekly signal counts — our own figures, as of September 2026