For cold email deliverability, the best fits are tools that check and fix sending health: InboxGuard scans SPF, DKIM, DMARC and blocklists and publishes DNS fixes 1020, Email-spam-tester gives a free spam score and authentication checks with optional inbox placement 2, and MailTester verifies addresses and tests inbox placement before sending 414. Full sending platforms such as Outreach2day, Warmerly and ColdSend cover mailboxes, warmup and sequencing 187.
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MailTester.commailtester.comverified and signed
Verifies single or batched addresses with a risk score and tests inbox placement, so bounces are caught before sending 414.
official:MCP server · MailTester Email Verification
for agents: Verify a small batch · Verify one email address
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Warmerlywarmerly.comwebsite read, tools not yet checked
Warms up Gmail and Microsoft 365 mailboxes to build sender reputation before cold outreach campaigns are sent 8.
official:MCP server · Warmerly
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Outreach2dayoutreach2day.comwebsite read, tools not yet checked
Provides cold email mailboxes, warmup, a sequencer and analytics showing which mailboxes reach the inbox, with an MCP server for setup 1.
official:MCP server · Outreach2day
Sources
- 1Cold Email Mailboxes That Reach the Inbox | Outreach2dayoutreach2day.com · read 2026-10-29
- 2Free Email Spam Tester — Spam Score & Inbox Placementemail-spam-tester.com · read 2026-10-29
- 4MailTester.com — Email Verifier & Deliverability Testmailtester.com · read 2026-10-29
- 7ColdSend – The simplest way to scale cold emailcoldsend.pro · read 2026-10-29
- 8Warmerly: Email Warmup and Cold Outreach, $19/mowarmerly.com · read 2026-10-29
- 10InboxGuard — Email deliverability monitoring & DMARC reportsinboxguard.io · read 2026-10-29
- 14MailTester: declares "Verify a small batch" (the record we read and signed)unfragile.ai · read 2026-10-24
- 20InboxGuard: declares "Scan domain deliverability" (the record we read and signed)unfragile.ai · read 2026-10-24
For agents: the 10 actions behind this answer
· Outreach2day website read, tools not yet checked
Cold email mailboxes, warmup and our own sequencer in one subscription for agencies and outbound teams, plus analytics that show which mailboxes land in the inbox.
· Email-spam-tester website read, tools not yet checked
Free email spam checker: send one message and get a SpamAssassin score, SPF, DKIM and DMARC checks, blocklists and optional inbox placement. No signup.
get_email_status · Resend (Activepieces) verified and signed
Get Email Status — Retrieve the delivery status of a sent email
Verify a small batch · MailTester verified and signed
Verifies up to 25 addresses per call and returns per-email verdicts. e.g. Clean this list of signup emails before I send the newsletter.
· Postbox Services website read, tools not yet checked
Expert email deliverability and email security consulting. 10+ years, 500+ clients, 5.0 Upwork rating. SPF, DKIM, DMARC, inbox placement, blacklist removal, anti-spoofing/BEC hardening and cold email infrastructure.
smtp · mailslurp-client verified and signed
· ColdSend website read, tools not yet checked
Cold email sequencer and the infrastructure it sends from, built together in one platform. IPs that self-manage, up to 100 mailboxes per domain, one price.
· Warmerly website read, tools not yet checked
Email warmup and cold outreach software. Warms up Gmail and Outlook mailboxes to build sender reputation, then sends your campaigns. From $19/month.
· Bento website read, tools not yet checked
Campaigns, automations, and transactional email on one platform. Every send is checked and paced, and our live delivery rates are public.
Scan domain deliverability · InboxGuard verified and signed
Run a full SPF/DKIM/DMARC/MTA-STS/TLS-RPT/BIMI/blocklist scan for a domain and return a 0–100 score with per-check findings. e.g. Is example.com set up correctly for DMARC? e.g. Why is mail from acme.io going to spam? e.g. Check if my domain is on any DNS blocklists.
Labels are the instruments' verdict and are never changed by ranking. Agents and robots get this same answer as JSON at /api/v1/find?q=…&answer=1 and through the MCP server.