An Email Deliverability Service Fixes Sending, Not Who You Send To

An email deliverability service works on the sending. It audits and repairs authentication, buys or retires domains, warms mailboxes, prunes the addresses that bounce, paces the volume, and reads the diagnostics when messages start being deferred or filtered. Every one of those is a real job, and a good service does them better than an agency doing it between client calls. None of them is a decision about who should receive the message.

The disclosure first. We build Keaz Signals, which sells buying signals and contacts for ecommerce outreach. We are not a deliverability service, we do not sell one, and we have no plans to. That makes us an interested party in this question rather than a neutral one, and the honest way to handle that is to say where the boundary sits and then say which side of it we are on.

The category is also wider than the word suggests. Some services are a one-off audit. Some are a retained consultant. Some are software with a human attached. Some are an agency that will run your sending infrastructure as a managed service. They are priced differently and scoped differently, but they all operate on the same layer — everything between your decision to write to someone and that message being accepted by a receiving server.

Google's sender guidelines are the closest thing this market has to a published specification, and they set the ceiling on what any service can honestly promise. The document requires SPF or DKIM, valid forward and reverse DNS for sending domains or IPs, a TLS connection, RFC 5322 formatting, and a spam rate reported in Postmaster Tools kept below 0.30%. Above 5,000 messages a day it adds SPF and DKIM both, a DMARC record, From: alignment and one-click unsubscribe (retrieved 20 September 2026).

The same page is blunter than most vendor marketing about what buying help gets you:

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.

There is no list to be added to. A service that implies otherwise is selling access that does not exist. What a service can do is make you meet the published requirements and keep you there — worth paying for, and not the same thing as inbox placement. The guidelines ask senders to keep spam rate below 0.10% and never reach 0.30%, and that number is produced by recipients clicking a button.

Four things are genuinely inside a deliverability service's authority, and each has a right answer an outsider can verify. If your problem is one of these, hiring someone is a good use of money.

1. Configuration: SPF, DKIM, DMARC, PTR records, alignment, TLS, unsubscribe headers. The part with a correct answer.
2. The domain and mailbox estate: how many of each, and which to retire because their reputation is spent.
3. Ramp and pacing: raising volume at a rate the receiving side tolerates, and cutting back when deferrals appear.
4. Diagnosis: reading SMTP errors, Postmaster Tools and blocklist status, and saying which is causing the drop.

The fourth earns the retainer. One symptom has several causes, and the docs cannot say which is yours. See What Email Deliverability Tools Can and Cannot Tell You.

A deliverability service cannot decide who belongs on the list, and that is the decision most sending problems trace back to. It is not a gap in the service's competence; it is outside the layer it operates on. Nobody auditing your DNS can know whether the store you are writing to has any current reason to care.

Google's own guidance puts the two next to each other. In the same document as the SPF and DKIM requirements, under sending practices, it says:

Don't purchase email addresses from other companies.

Don't send messages to people who didn't sign up to get messages from you.

Those lines sit beside the technical requirements because they govern the same outcome. Spam rate is the number everything is measured against, and recipients produce it. Configuration stops you being rejected; it does not stop you being reported. That is a structural point about where each layer's authority ends, not a claim about anyone's compliance.

Google also notes that it does not track open rates and cannot verify third-party open-rate reporting (retrieved 20 September 2026) — worth knowing before you accept an open rate as evidence that a fix worked.

The quickest way to tell the two apart: ask whether messages are being rejected or being ignored. Rejection, deferral, authentication failures and blocklist entries are sending problems, and a service fixes them. Messages that arrive and do nothing are a list problem, and no amount of configuration changes that.

Three symptoms point clearly at the sending layer: SMTP errors naming authentication or reverse DNS, a domain reputation that fell without a change in who you were writing to, and a spam rate that rose across every campaign at once. Hire for those.

Three point at the list: replies that say the timing is wrong, spam complaints concentrated in one segment, and a setup that was clean until volume went up against the same audience. A wider pipe pointed at the same people delivers the same unwanted message faster. We took the throughput version of that apart in A Bulk Email Sender Solves Throughput, Not Timing.

We are the wrong purchase for a lot of people reading this, and it is cheaper for both of us to say so here. If your authentication is broken, your domains are burned or a receiving server is deferring you, buy the service. Nothing we sell touches any of that, and we would be taking your money for the wrong problem.

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 — no other platform, no other market. Registry, firmographic and hiring triggers are marked planned on our own site, which means they do not exist yet.

We are GDPR-conscious by design and will not claim more than that; responsibility for what you send stays with you. We also sell no domains, mailboxes, SMTP, warmup pool or sequence engine. Sending runs through Instantly, in your own workspace, on your own domains — which means the reputation you build stays yours, and so does the responsibility for it. The layer underneath is the subject of What Email Infrastructure Does, and What It Cannot Decide.

We are not going to tell you what inbox placement rate a deliverability service will get you. We did not measure it, we could not measure it without running the same campaigns twice under controlled conditions, and any figure we published would travel further than the caveat attached to it.

We are also not going to tell you how much a signal-led list improves deliverability. That is the claim this article comes closest to being able to make, and it is the one we cannot make: it would need the same team, same offer, same domains, same week, one variable changed. We have not run that experiment.

And we make no deliverability or reply-rate promises of any kind, nor will we quote anyone else's coverage or accuracy figures at you without their own published, dated source. The refusal is the point rather than an aside: the claims we cannot support are exactly the ones this category is loudest about.

Wired together, the service keeps the sending healthy and the layer above decides who is worth writing to. A segment defines the kind of store you sell to. A signal decides which store is worth a message this week. Warmup and monitoring sit on the service's side of that line — see Email Warmup Ramps Toward Limits Nobody Publishes.

As of September 2026 we watch 4.1 million Shopify and WooCommerce stores, re-scraped weekly, and roughly 41,200 carried a fresh signal in the last seven days. Our own figures; they move, which is why they are dated. The buying signal catalogue lists what we watch for, and the ecommerce leads database is where those stores arrive with contacts attached. Signup includes 1,000 free leads.

• Email sender guidelines, Gmail Help — authentication and DNS requirements, spam-rate thresholds, sending practices, the allowlist statement and the note on open rates, retrieved 20 September 2026
• Set up Postmaster Tools, Gmail Help — what the dashboards report on spam rate, reputation, authentication and delivery errors, retrieved 20 September 2026
• Keaz Signals store coverage and weekly signal counts — our own figures, as of September 2026
• Keaz Signals product scope, including what is not shipped — our own buying signal catalogue, retrieved 20 September 2026