IONOS (1&1) Email Verification
IONOS, formerly 1&1, is a major European hosting provider whose mail platform powers business email on many custom domains.
How IONOS (1&1) Handles Verification
IONOS-hosted mail usually rejects unknown recipients with a 550 at the SMTP level, so mailbox existence is verifiable for most domains, unless the domain owner has enabled a catch-all. Greylisting and rate limiting apply.
What Mailthentic does
We perform the SMTP handshake, interpret the RCPT TO response, run a catch-all probe to detect accept-all domains, and apply greylisting retries for accurate results.
Quick Facts
MX Pattern
mx0*.ionos.com / mx0*.kundenserver.de
Catch-All Behavior
Rejects unknown addresses
Typical SMTP Response
550 for unknown recipients on most domains (verifiable)
Provider Type
business
Common Domains
varies (custom domains hosted on IONOS)
Best Practices for IONOS (1&1)
- SMTP results are usually reliable. A 550 generally means the mailbox does not exist.
- Check for catch-all. Some IONOS domains accept every address.
- Handle greylisting. Retry deferred attempts after a short delay.
Other Email Providers
Verify IONOS (1&1) email addresses
Our 9-point verification engine handles IONOS (1&1)'s specific behavior automatically. Start free.