Catch-All Provider
consumer
ProtonMail Email Verification
ProtonMail (now Proton Mail) is a privacy-focused email provider based in Switzerland. It prioritizes user privacy, which extends to how it handles verification probes.
How ProtonMail Handles Verification
ProtonMail accepts all RCPT TO commands with 250 OK, regardless of mailbox existence. This is a deliberate privacy measure — ProtonMail will not reveal which addresses are registered.
SMTP verification is completely ineffective for ProtonMail addresses. There is no way to confirm individual mailboxes via SMTP.
What Mailthentic does
- Detects ProtonMail via MX records
- Skips SMTP verification (always returns 250, provides no signal)
- Performs DNS-level checks only
- Returns "deliverable_unconfirmed" with a note about privacy-focused provider
Quick Facts
MX Pattern
mail.protonmail.ch
Catch-All Behavior
Accepts all addresses
Typical SMTP Response
250 OK for all RCPT TO
Provider Type
consumer
Common Domains
protonmail.com
proton.me
pm.me
Best Practices for ProtonMail
- You cannot verify individual ProtonMail addresses via SMTP. This is by design.
- Use double opt-in. The only way to confirm a ProtonMail address is to have the user click a confirmation link.
- ProtonMail users are typically high-quality. They chose a paid/premium privacy-focused service — they're unlikely to be spam signups.
- Check syntax and domain only. Ensure the address format is valid and the domain is real.
Other Email Providers
Verify ProtonMail email addresses
Our 9-point verification engine handles ProtonMail's specific behavior automatically. Start free.