Dev tools · alternatives · 2026

24 alternatives to SMTP Field Manual

A collection of SMTP error codes from major inbox providers.

Below are 24 products that do a similar job, ranked by how close each is in meaning and then by launch-day votes. SMTP Field Manual launched in 2019; newer entries below may have overtaken it.

1. 1
   SMTP Debug Tool▲346

   Test and debug your SMTP connection, quickly and for free

   2023 · its alternatives →

2. 2
   mailX by mailwarm▲602

   Email deliverability toolkit for humans and AI agents

   May 2026 · themailx.com · its alternatives →

3. 3
   Mailwarm 2.0▲683

   The email warmup tool, upgraded for deliverability.

   Jun 2026 · mailwarm.com · its alternatives →

4. 4
   RealMail▲365

   The email validation for SaaS

   2024 · realmail.dev · its alternatives →

5. 5
   Email Testing By Inbox Pirates▲358

   Preview, analyze & test emails with one click

   2022 · its alternatives →

6. 6
   MailAdept by mailwarm▲287

   AI Agents & Email deliverability experts on your team

   Jul 2026 · mailadept.com · its alternatives →

7. 7
   Unspam.email▲309

   Email spam checker and newsletter heatmap prediction.

   2020 · its alternatives →

8. 8
   Mailook▲315

   Identify & fix your email deliverability issues for free

   2021 · its alternatives →

9. 9
   Email Spam Checker by Autoklose▲105

   Send spam-free, high-converting emails

   2020 · its alternatives →

10. 10
    SMTP‑Test.com▲103

    One‑click SMTP server test with real‑time protocol logs

    2025 · smtp-test.com · its alternatives →

11. 11
    DevMail▲183

    Email sandbox for software developers

    2024 · its alternatives →

12. 12
    Lob▲106

    Programmatically send physical mail and verify addresses

    2013 · its alternatives →

13. 13AF
    A fake SMTP server for software integration testing▲127

    This is a side project of mine. Use this as your SMTP server in a test environment to guarantee that your users don't receive test emails. Looking for feedback, especially on the security side.

    2024 · fakemail.stream · its alternatives →

14. 14
    SMTP Email Verifier▲7

    Check email lists with syntax, MX, and SMTP verification

    Jun 2026 · apify.com · its alternatives →

15. 15
    Email Blocklist Checker▲20

    Emails Landing in Spam? 1-click to know what went wrong.

    2020 · its alternatives →

16. 16EE
    Email encoder – protect your public emails from bots and crawlers▲19

    2022 · freetools.dev · its alternatives →

17. 17
    EmailAddress.ai▲9

    Verify Catch-all Emails with confidence

    2025 · emailaddress.ai · its alternatives →

18. 18SV
    Self-Validating Email Aliases for Postfix▲28

    2019 · github.com · its alternatives →

19. 19
    MailFrom.dev – A sandbox SMTP for devs▲17

    Easily test emails. No real delivery. No complex setups.

    2025 · mailfrom.dev · its alternatives →

20. 20
    smtp-probe▲2

    Go CLI for email deliverability diagnostics

    Jul 2026 · github.com · its alternatives →

21. 21
    Recipient Validation▲20

    Data-driven email validation powered by SparkPost.

    2019 · its alternatives →

22. 22
    SMTP Ghost▲9

    Cold email marketing software without the ridiculous price

    2025 · smtpghost.com · its alternatives →

23. 23
    MailTested▲7

    Check why your emails go to spam — instantly.

    Nov 2025 · mailtested.com · its alternatives →

24. 24
    Email Copy Checker▲5

    Check your emails for spam trigger words before hitting send

    2017 · its alternatives →

Ranked by how close each launch is in meaning, then by votes. Prices were read from each product’s own site when checked and can change. Refine with your own description →