There is no single objectively “best” SMTP provider for everyone in 2025; the top choice depends on whether you care most about deliverability, price, ease of use, or enterprise features.

Based on recent independent comparisons and 2025 reviews:

• Best pure deliverability (tested):

  • SMTP2GO scored the highest average deliverability (≈96%) in EmailToolTester’s 2025 tests, ahead of Postmark and others.1
  • Postmark consistently ranks at or near the top in deliverability-focused comparisons and is often listed as a top SMTP service for reliability and inbox placement.1245

• Best for developers / APIs & scale:

  • Mailgun, SendGrid, and Amazon SES are repeatedly recommended for large-scale transactional email, good APIs, and scalability.23456
  • Amazon SES is often cited as the cheapest at scale (very low per‑email cost) but with a more complex, DIY-style setup.45

• Best for “all‑in‑one” marketing + SMTP:

  • Brevo (Sendinblue) and Mailjet are highlighted for combining SMTP with marketing automation, SMS, CRM, etc., and being beginner‑friendly.12467

• Best for WordPress / ease of use:

  • SendLayer is WPBeginner’s #1 recommended SMTP mailer service in 2025 for WordPress users, emphasizing simplicity and reliability.6

In practice, if you want a single strong general‑purpose pick for transactional email in 2025 and are not extremely price‑sensitive, Postmark and SMTP2GO are frequently at the top for deliverability and reliability.1245
If you are optimizing mainly for cost at high volume, Amazon SES is usually the best value, with Mailgun and SendGrid as common alternatives.245

If you tell me your main use case (transactional vs marketing, approximate volume, budget, technical comfort), I can narrow this down to one or two concrete recommendations.