Email Deliverability Tools, Sorted by the Job They Do

Email deliverability tools fall into seven jobs: authentication checkers (SPF, DKIM, DMARC), blocklist monitors, mailbox provider dashboards such as Google Postmaster Tools and Microsoft SNDS, DMARC report analysers, seed or inbox placement testers, warmup tools, and list verification. No single tool does all seven. Pick by the question you need answered.

Roundups usually rank products. That is less useful than it looks, because a seed tester and a blocklist monitor answer completely different questions. This guide groups tools by job, says what each kind can and can't tell you, and only states vendor details we checked on the vendor's own page on 8 October 2026.

The quick map

Your question	Tool type	Examples
Are my DNS records right?	Authentication checker	Our SPF, DKIM and DMARC checkers
Is my IP or domain blocklisted?	Blocklist checker or monitor	MxToolbox, our blacklist check
How does Gmail see my mail?	Provider dashboard	Google Postmaster Tools
How does Outlook.com see my IPs?	Provider dashboard	Microsoft SNDS
Who is sending as my domain?	DMARC report analyser	Postmark DMARC digests, GlockApps
Where does this message land?	Seed / placement test	GlockApps, mail-tester
Is my new inbox building history?	Warmup	Instantly, lemlist's lemwarm
Will these addresses bounce?	Verification	Any email verifier

Authentication checkers

These read your public DNS and tell you whether SPF, DKIM and DMARC exist and are valid. They are the first thing to run, because a broken record makes every other result meaningless. Since 1 February 2024, Google's sender guidelines have required everyone sending to Gmail accounts to "Set up SPF or DKIM email authentication", and senders of more than 5,000 messages a day to have SPF, DKIM and DMARC.

What they can't tell you: whether your real messages pass alignment. A record can be valid and still not match the domain your email platform signs with. For that, look at the Authentication-Results header of a message you actually sent; our email header analyzer reads it in your browser. The deliverability audit runs MX, SPF, DKIM, DMARC and blocklist checks for a domain in one pass.

Blocklist checkers and monitors

A blocklist checker queries DNS-based blocklists for your sending IP or domain; a monitor repeats that on a schedule and alerts you. MxToolbox's tool says it tests "a mail server IP address against over 100 DNS based email blacklists." GlockApps' free plan includes one IP reputation monitor.

Two cautions. First, lists are not equal: some are queried by a large share of receiving servers, others by almost nobody, so a single hit on an obscure list is rarely the reason mail is failing. Read the list's own documentation before panicking. Second, if you send through a shared platform, the IP may not be yours to fix. Check the domain too.

Google Postmaster Tools

Postmaster Tools is Gmail's own view of your sending, and nothing else gives you that. Google's dashboard documentation lists compliance status, spam rate, IP and domain reputation, feedback loop, authentication, encryption and delivery errors. You have to verify the domain before its data appears.

The main limitation is volume. Google says that "dashboards might not include all data on days when your outgoing email volume is low." A small cold email operation may see little or nothing. When data does appear, spam rate is the line to watch: Google asks senders to stay below 0.3%. Our Postmaster Tools guide explains each dashboard.

Microsoft SNDS

Smart Network Data Services shows Outlook.com's view of IP addresses you control. The SNDS FAQ describes it as an initiative for "everyone who owns IP space", with data including recipient counts, spam filter verdicts shown as green, yellow or red, and complaint rates. Access is granted through an automated process that sends an authorisation email to an address tied to the IP range.

That ownership requirement is the catch. If you send through Google Workspace, Microsoft 365 or a shared ESP pool, you don't control the IP and can't register it. SNDS is mainly useful to teams on dedicated IPs. Its FAQ describes data from Outlook.com's mail servers; it says nothing about Microsoft 365 business tenants, so don't expect it to explain corporate rejections. The FAQ is also clear that "the SNDS system merely displays the data which affects delivery"; it isn't a support channel.

Yahoo offers a Complaint Feedback Loop instead of a dashboard: enrol your DKIM signing domain and Yahoo sends you a report when a user marks your mail as spam.

DMARC report analysers

DMARC aggregate reports arrive as XML files from receiving providers; an analyser turns them into a list of who sent mail as your domain and whether it passed. This is how you find a forgotten tool sending unauthenticated mail before you move DMARC to quarantine or reject.

Postmark's DMARC digests are described on its page as "A free weekly email to help monitor & implement DMARC." GlockApps' free plan includes DMARC analytics for 10,000 messages a month. Start with p=none, read the reports until every legitimate sender passes, then tighten the policy.

Seed and inbox placement testers

A seed test sends one real message to monitored mailboxes and reports whether each copy landed in the inbox, a tab, spam, or nowhere. It is the quickest way to check whether a specific message or a DNS change caused a problem.

• GlockApps' pricing page lists a free plan with 2 inbox placement test credits a month.
• mail-tester gives you an address to send to and a scored report. Its FAQ says "You can perform 3 tests for free within the last 24 hours."

The limitation is that seed mailboxes have no history with you, and Gmail personalises filtering by user. A seed result describes those accounts, not your recipients. Read inbox placement seed tests before acting on one.

Warmup tools

Warmup tools send, open and reply to messages between your inbox and a network of other inboxes to build sending history. Instantly's warmup page says its warmup "sends, receives, opens, and replies to emails between your connected accounts and its warmup network." lemlist's lemwarm "automatically exchanges real emails with real inboxes to build your sender reputation."

What nobody can tell you is how much this counts. No major mailbox provider has published how it treats warmup traffic. Use it as a supplement to slowly sending real mail to people likely to engage, not as a replacement. Google's sender guidelines do carry one relevant warning: "immediately doubling previously sent volumes suddenly could result in rate limiting or reputation drops." Ramp gradually whatever tool you use.

Email verification

Verification checks each address before you send and removes the ones that would hard bounce. It is the only tool in this list that works on your list rather than your infrastructure. Mailbox providers watch bounce rates, and Gmail's help page even names bounces to invalid addresses as a reason it can block a personal account from sending.

A verifier can't fix authentication or content. What it can do is stop a dirty list from undoing the work the other tools support. For single addresses there is our free email checker; the free list health check on the same tools page finds duplicates, typos and dead domains in a CSV in your browser. SimpleVerifier's paid plans handle full-list SMTP verification; see pricing. Whichever verifier you use, check how it reports catch-all domains, because those addresses can't be confirmed either way.

A sensible order

1. Fix DNS first: SPF, DKIM, DMARC, and a PTR record if you run your own server.
2. Clean the list before the first send.
3. Check blocklists for your sending IP and domain.
4. Turn on Postmaster Tools and, if you own the IPs, SNDS. Enrol in Yahoo's feedback loop.
5. Seed test after any change to infrastructure or templates.
6. Read DMARC reports weekly until you reach p=reject.

Most deliverability problems show up in one of those steps. The tools only help if you use the right one for the question.