How Important Is SMTP Mailbox Verification?

I'm curious to hear everyone's thoughts and experiences with SMTP mailbox verification.

Many email verification services claim to verify whether an email address actually exists by performing SMTP-level checks with the recipient's mail server. While this sounds useful, I've noticed that many major email providers (such as Gmail, Microsoft, Yahoo, etc.) have become much stricter and often don't reveal whether a mailbox exists.

A few questions I'd love to discuss:

• How reliable is SMTP mailbox verification in 2026?

• Does it still significantly improve email list quality, or is it becoming less effective?

• How do you handle providers that always return "accept-all" or block verification attempts?

• Have you found that SMTP verification reduces bounce rates in real-world email campaigns?

• Are there any best practices or techniques that improve accuracy without harming the sender's reputation?

• For those building email verification platforms, how much weight do you give SMTP verification compared to syntax validation, MX record checks, disposable email detection, domain reputation, and historical data?

From my perspective, SMTP verification seems to be just one piece of the puzzle rather than a definitive answer.

With increasing privacy protections and anti-enumeration measures, I'm wondering whether the industry is moving toward a more risk-scoring approach instead of relying heavily on SMTP responses.

I'd really appreciate hearing from people who have built email verification systems, run large-scale email campaigns, or have data comparing SMTP verification against actual delivery results.

Looking forward to your insights and experiences!