Best email authentication tools in 2026, compared

The best email authentication tools are the ones that match what you actually need to check: a mailbox provider's reputation view, a one-off DNS record lookup, or ongoing DMARC monitoring across the domains you manage. This article compares 5 tools against clear criteria, sets out what each covers, and gives each one's pricing where we could confirm it. The mistake to avoid: treating a list-cleaning or warmup tool as a substitute for DMARC monitoring, when it checks something else entirely.

How we judged the best email authentication tools

We judged the tools below on 4 things: which layer of the stack each one covers, a DNS record, mailbox-side reputation, or protocol monitoring; whether the check is a one-off lookup or continuous monitoring; whether it is free or paid, and how the pricing works; and whether UK or GBP pricing or hosting is published. SPF, DKIM and DMARC are the 3 protocols that let a receiving mail server check whether a message really comes from your domain, as set out in RFC 9989 and NCSC's anti-spoofing guidance.

Mailwarm's own "best email authentication tools" list puts Mailwarm, a warmup service, in first place, and list-verification tools belong in the same separate category. Those check whether an address is real, or build up sender reputation through engagement, which is a different job from checking SPF, DKIM and DMARC records. We have kept that distinction below and flagged the one entry that falls into the other category.

This matters more than it used to. Gmail and Yahoo began enforcing SPF, DKIM and DMARC for bulk senders from February 2024 (Google, Yahoo), and Microsoft brought in similar rules from May 2025 for domains sending more than 5,000 emails a day to its consumer Outlook.com, Hotmail and Live addresses (Microsoft). DMARC enforcement, a policy of p=quarantine (send fakes to spam) or p=reject (refuse fakes), lets a receiver act on mail that fails authentication while using your exact domain in the From address. It does not stop lookalike domains or display-name spoofing, which need separate monitoring.

If you need the basics first, our guide to what DMARC is covers the background. If you already know you want a DMARC platform specifically, rather than any category below, our best DMARC monitoring tools guide compares those head to head.

Google Postmaster Tools: free Gmail-side reputation monitoring

Google Postmaster Tools shows how Gmail sees your domain, for free, with no equivalent view for any other receiver.

• What it does well: a free dashboard showing SPF, DKIM and DMARC pass rates, spam-rate analytics, delivery errors and compliance with Gmail's sender requirements, specifically for mail landing in Gmail (source).
• Limits: it only shows Gmail's view of your mail, with no visibility into Outlook, Yahoo or any other receiver, and Google says its domain and IP reputation dashboards will be retired.
• Pricing model: free, with no paid tier.
• Best for: any organisation sending real volume to Gmail addresses, used alongside a DMARC monitor rather than instead of one.

Microsoft SNDS: free Outlook and Hotmail reputation monitoring

Microsoft's Smart Network Data Services does for Outlook.com and Hotmail roughly what Google Postmaster Tools does for Gmail.

• What it does well: a free reputation feed per sending IP, covering spam filter results and complaint rates for Outlook.com and Hotmail, and it includes Microsoft's Junk Email Reporting Program, which sends you reports when users mark your messages as junk (source).
• Limits: it covers only Microsoft's consumer mail addresses, not Microsoft 365 tenants, Gmail or Yahoo, and it does not validate SPF, DKIM or DMARC records.
• Pricing model: free, registered per sending IP range.
• Best for: senders with meaningful volume to Outlook.com or Hotmail addresses, as one input among several rather than a DMARC monitor.

MXToolbox: one-off DNS and record diagnostics

MXToolbox answers a single question well: what does this domain's SPF, DKIM and DMARC record say right now.

• What it does well: validates SPF, DKIM and DMARC records, runs real-time DNS lookups and checks many blocklists in one search (source, blocklist check).
• Limits: its free lookups are point-in-time checks that will not alert you when a record changes or a DMARC policy weakens, and the one monitor on its free plan only checks 30 blocklists; record monitoring and DMARC management need a paid plan (pricing).
• Pricing model: free for single lookups and one monitor, with paid plans for more monitors and for DMARC management: Delivery Center costs $129 a month and Delivery Center Plus $399 a month, each for 5 domains (pricing).
• Best for: a quick manual check while building or debugging a record. ShieldMarc's own free DMARC checker and email header analyser do the same one-off job, alongside separate SPF and DKIM checkers.

ShieldMarc: ongoing DMARC monitoring with the wider record set included

ShieldMarc turns DMARC reports into continuous monitoring, then adds DNS, certificate and expiry checks, which the free tools above cover only partly, if at all.

• What it does well: continuous DMARC aggregate and forensic report processing, plus an A+ to F Security Grade built from 16 outside-in checks spanning SPF, DMARC, SSL, MTA-STS, TLS-RPT, DNSSEC and CAA. DKIM is not part of the grade.
• Limits, stated plainly: no partner or reseller programme, no PSA integrations, no hosted BIMI, no SOC 2, ISO 27001 or Cyber Essentials certificate today, no live SMTP STARTTLS test, and no Slack, Teams or webhook alerts.
• Pricing model: Starter is free with no time limit, for 1 domain, DMARC reports and 1 SSL monitor. Professional is £70 a month, or £50 a month billed annually, for 25 domains. MSP is £130 a month, or £100 a month billed annually, for 100 domain slots. Every sign-up starts a separate 30-day trial with no card, covering 10 domains and every module except Dynamic SPF (pricing).
• Best for: UK MSPs and IT teams who want DMARC monitoring plus the DNS, certificate and expiry checks the free tools above only partly cover.

Pro Tip: Check your Security Grade again after any DNS change: the dashboard recalculates it daily at 02:03 UTC and when a DMARC policy changes.

ShieldMarc's real position is as one platform among several UK-relevant options for DMARC monitoring, not the only one. Readers who have already decided they want a DMARC platform specifically should compare monitoring platforms directly rather than take this listicle as that comparison.

My honest view: if your only need is a single DMARC record check, use a free tool above and stop there. ShieldMarc is for what happens next, the reports that keep arriving once the record is live, and the certificate, DNSSEC or expiry check that a one-off lookup will not repeat for you next month.

Mailwarm: a warmup tool, not a DMARC platform

Mailwarm solves a different problem: getting mail into the inbox once authentication is already configured, not authentication itself.

• What it does, per its own description: a premium email warmup and deliverability platform that bundles some authentication fix tooling, built to improve inbox placement through engagement (source).
• Limits: it is not built to parse DMARC aggregate reports or track policy enforcement over time, so it cannot substitute for a DMARC monitor.
• Pricing model: warmup plans are paid only, from $69 a month billed annually for one mailbox, with larger and custom plans above that (pricing). Its separate SPF, DKIM and DMARC checkers are free with no sign-up (free tools).
• Best for: senders whose problem is inbox placement after authentication is already configured correctly. Its first place on its own "best email authentication tools" list is a category mismatch worth flagging to readers.

Email authentication tools compared

The table below lines up all 5 tools on the same 4 points: primary job, one-off or ongoing, cost, and best for.

Google Postmaster Tools and Microsoft SNDS are free with no paid tier at all. MXToolbox and ShieldMarc are freemium: a free layer, then a paid tier for more. On the last of our four criteria, only ShieldMarc publishes prices in GBP, while MXToolbox and Mailwarm price their paid plans in US dollars, and ShieldMarc's standard hosting is in Germany, not the UK. Mailwarm is a different job entirely, and the list that ranks it first is Mailwarm's own.

The free mailbox tools each show one receiver's view, and a one-off lookup does not repeat itself, which is exactly the gap ongoing monitoring is built to close.

How to choose the right tools for your situation

Which tools you need depends on who your mail reaches and how many domains you manage, not which list ranks highest.

A single domain sending mostly to Gmail and Outlook.com recipients should pair Google Postmaster Tools, plus Microsoft SNDS if it sends from IP addresses it is responsible for, with a free DMARC checker and DMARC report monitoring from the start. Watch the reports at p=none until every legitimate service sending as your domain passes, then move to p=quarantine (send fakes to spam), as NCSC guidance recommends.

An MSP managing many client domains cannot rely on reputation dashboards, which do not scale per client. Per-domain monitoring and reporting matters more than any single free checker once you are past a handful of domains (DMARC for MSPs).

A UK public sector body that relied on NCSC Mail Check needs continuous DMARC report processing and ongoing record checks, not a one-off diagnostic tool: Mail Check stopped DMARC aggregate reporting on 24 March 2025, and its checks of DMARC, SPF, MTA-STS and inbound TLS settings ended when it closed on 31 March 2026 (NCSC, NCSC retirement notice).

Anyone still mid-setup should use the free record generators and checkers first, before paying for monitoring. Publish SPF, DKIM and a DMARC record at p=none with a rua= address, then use the reports to find every service sending as your domain before you tighten the policy.

One assumption worth correcting: Cyber Essentials does not require DMARC, SPF or DKIM. Choose a tool based on what receivers actually do with your mail, not a certification requirement.

Start today

3 steps take you from unclear to monitored: check what you have, fix any gap, then use ongoing DMARC reports to confirm every service sending as your domain passes before you tighten the policy.

Run the free Domain Trust Check for an A+ to F grade across 16 checks before you choose a tool. It shows what is already in place and what is missing across those checks in one lookup, but it does not check DKIM, so use the free DKIM checker for that.

Generate any missing SPF or DMARC record with the free DMARC generator and the matching SPF generator, then publish the records in your DNS. For DKIM, Microsoft 365 and Google Workspace create the key for you and show you the records to publish (Microsoft's DKIM guide); use the free DKIM generator, set to RSA 2048-bit, only where your mail system lets you add your own key.

If ongoing DMARC reports are what you are missing, start a 30-day ShieldMarc trial with no card, and expect the first reports within 24 to 48 hours of adding its reporting address to your DMARC record's rua= tag. If you still rely on NCSC Mail Check, treat a replacement as the next step rather than an optional one: it closed on 31 March 2026, and that date is already behind us.

Frequently asked questions

What is the best free email authentication tool?

There is no single best free tool. Google Postmaster Tools and Microsoft SNDS are both free, but each shows only one receiver's view of your mail. ShieldMarc's Starter plan is free with no time limit, for 1 domain, with DMARC report processing and 1 SSL monitor, which neither mailbox tool offers. Pick based on which receivers your mail actually goes to, rather than looking for a single ranked winner.

Is SPF, DKIM or DMARC enough on its own?

No single one is enough. SPF authenticates the sending IP address and DKIM authenticates the message signature, but neither tells a receiver what to do when a check fails. DMARC (RFC 9989) ties SPF and DKIM to the From address, sets the policy, and is the only one of the 3 that asks receivers for aggregate reports. NCSC guidance recommends configuring all 3 together, and DMARC reports come only from receivers that send them, so no single report proves total coverage.

Does Cyber Essentials require these tools?

No. Cyber Essentials does not require DMARC, SPF or DKIM. Our Cyber Essentials and email security guide sets out what the scheme does require instead, and what UK public sector buyers ask their suppliers about email security. The records still matter for other reasons, such as spoofing and brand abuse, even without a certification requirement behind them.

What replaced NCSC Mail Check?

Nothing automatic. NCSC Mail Check closed on 31 March 2026, and it had already stopped DMARC aggregate reporting on 24 March 2025 (NCSC), so organisations that relied on it for DMARC reports need a replacement platform rather than a one-off checker to receive those reports again. Our guide to migrating from Mail Check and the NCSC Mail Check retirement guide cover the practical steps.

Can one tool check SPF, DKIM and DMARC together?

Yes, to a point. MXToolbox offers separate free SPF, DKIM and DMARC lookups, while ShieldMarc's free DMARC checker validates a DMARC record and analyses SPF in a single lookup. ShieldMarc's checker does not look up the DKIM key itself, though: its separate DKIM checker probes a fixed list of selectors, plus up to 10 you type, and reports only whether each publishes a key, so 2 free tools are needed to cover all 3 records.

Sources

• RFC 9989: DMARC (May 2026)
• NCSC: Email security and anti-spoofing
• NCSC: Mark spoof emails as spam
• Google: Email sender guidelines
• Yahoo: Sender best practices
• Microsoft: Outlook's new requirements for high-volume senders
• Microsoft: Outlook.com services for senders (SNDS and JMRP)
• MXToolbox: SuperTool
• MXToolbox: plans and pricing
• Mailwarm's own listing: 10 Best Email Authentication Tools for 2026
• Mailwarm: pricing
• Mailwarm: free email deliverability tools
• NCSC: Mail Check update
• NCSC: Retiring Web Check and Mail Check

Related reading

• DMARC Monitoring Pricing in GBP, from Free
• Why ShieldMarc: MSP Edge in Domain Security
• Migrate from NCSC Mail Check
• TLS certificate chain errors: causes and fixes
• CAA record management: syntax, checks and fixes
• How to read a DMARC RUA XML report