Domain name

The domain is sent to the petuja.tools server, which queries its configured DNS resolver.

What this tool does

Query the domain’s published MX records and inspect the mail targets in ascending preference order.

Distinguish explicit MX records, a valid Null MX and the SMTP fallback that can apply when no MX exists.

Enter a domain without a protocol, path, email address or port.
Run the lookup and review record type, preference, target and MX TTL.
Compare the returned IPv4 and IPv6 addresses for each usable target.
Read the notices carefully when the result uses implicit fallback or contains an invalid Null MX combination.

Lower MX preference numbers are tried before higher numbers; equal values are equally preferred and sending systems may randomize them.
If no MX exists, SMTP can treat the domain itself as an implicit MX target when address records are available.
A valid Null MX consists solely of preference 0 and target “.” and means that the domain does not accept email.
The lookup uses the petuja.tools server resolver, does not validate DNSSEC and can differ from other resolvers because of caching or network location.

Does a missing MX record always stop email delivery?

No. SMTP may fall back to the domain’s A or AAAA records when no MX record exists.

Does the lowest number mean the fastest server?

No. It means the server is preferred first; it does not measure latency or capacity.

What happens when two MX records have the same preference?

They are equally preferred. Sending mail systems may distribute attempts between them.

Does the tool test SMTP connectivity?

No. It reads DNS records and resolves addresses but does not connect to port 25 or verify mail acceptance.

Are queries private to my browser?

No. The submitted domain is processed by the petuja.tools server and its configured DNS resolver.