so-net.ne.jp email servers, SPF and DMARC

so-net.ne.jp publishes a single MX host, ms-ext91.so-net.ne.jp. With no backup host, a sender that can't reach it queues the message and retries until the server answers or the queue gives up.

The record on 5 November 2026 was v=spf1 ip4:202.213.234.0/24 exists:%{i}.spf.so-net.ne.jp include:spf.xspmail.jp include:a.spf.nuro.jp include:spf-bma.mpme.jp include:spf-rmb.mpme.jp include:amazonses.com ~all.

In plain terms, it delegates to spf.xspmail.jp, a.spf.nuro.jp, spf-bma.mpme.jp, spf-rmb.mpme.jp and amazonses.com and lists 1 IP range directly. The top level uses 6 DNS-querying terms; SPF allows 10 in total including nested includes (RFC 7208 §4.6.4).

It ends in a soft fail (~all): mail from unlisted servers should be accepted but treated as suspicious.

The record is v=DMARC1; p=reject; ri=14400; rua=mailto:[email protected].

p=reject asks receivers to refuse mail that fails DMARC.

Aggregate reports go to so-net.ne.jp, so the domain's owner sees who sends mail as @so-net.ne.jp.

What that means for you: if a contact gives an @so-net.ne.jp address and you send to them, nothing changes. But never put an @so-net.ne.jp address in the From line of mail sent through your own tool or ESP. It can't pass DMARC for so-net.ne.jp, and this policy tells receivers to refuse it.

Our checker treats @so-net.ne.jp like any domain: syntax, MX, disposable and role checks first, then a made-up address to rule out a catch-all, then your address at RCPT TO, disconnecting without sending. We have not published a test of how ms-ext91.so-net.ne.jp answers for @so-net.ne.jp, so we make no claim here about whether single mailboxes can be confirmed; each result carries its own reason.

DNS tells you where mail goes, not whether one person's mailbox still exists. For a list, run the whole file through a verifier before you send: invalid rows come out, risky rows (catch-all, unknown, refused) go in their own segment, and valid rows are safe to mail.