Yandex runs the largest mailbox service in the Russian-speaking world: consumer Yandex Mail on yandex.ru and its sister domains, and Yandex 360 for Business for company domains. Business domains point their MX at mx.yandex.net and Yandex's own consumer domains at mx.yandex.ru; Spaw matches both and reports mx_provider: "yandex".
How Yandex shows up in DNS
Yandex 360 for Business asks domain owners to publish one MX record, mx.yandex.net at priority 10, or to delegate the domain to Yandex's DNS, which configures it automatically. Spaw matches the .yandex.net suffix, and the .yandex.ru suffix that Yandex's own consumer domains, including yandex.com and yandex.ru, currently resolve to. Yandex is a mailbox host: mx_found is true and mx_implicit is false for a correctly configured business domain.
How Yandex answers a verification handshake
Yandex typically rejects unknown recipients at RCPT TO, so most business-domain checks settle on the first attempt. Its inbound servers are cautious with senders they have not seen and can defer a first connection, which leaves some probes unverified with smtp_reason: greylisted. A Yandex 360 administrator can configure a catch-all mailbox per domain, and those domains answer as catch-all.
What that means for your verdicts
Expect deliverable with mailbox_exists: true, undeliverable with reason: mailbox_not_found and smtp_reason: no_mailbox, or risky with reason: catch_all on domains with a catch-all mailbox. For catch-all domains Spaw returns mailbox_confidence, which without the established-provider bonus is driven by the domain's DMARC and SPF, its registration age, the shape of the username and your own delivery outcomes. There are no consumer username rules for Yandex domains in Spaw's rule set, so invalid_local_part does not apply; the RFC syntax check still does, and Cyrillic domain names are converted to their punycode form before any lookup.
SPF and DMARC at Yandex
Yandex 360's documentation gives v=spf1 redirect=_spf.yandex.net as the SPF record when Yandex is the only sender, or v=spf1 ip4:... include:_spf.yandex.net ~all when other servers send too, and it provides a DKIM key from the admin console. Delegated domains get these records automatically. Spaw reports the live state in has_spf and dmarc_policy; a business domain without SPF adds ten risk points to its addresses.
Practical notes for sending to Yandex users
Yandex's filtering leans on sender authentication and on its own reputation data, and it expects List-Unsubscribe headers from bulk senders in the same way the large western providers do. Many Yandex-hosted business domains use Cyrillic or transliterated usernames; Spaw's name dictionary is English-centric, so is_gibberish is more likely to be wrong on these lists and should be treated as a hint rather than a rule. Plus-addressing is supported and reported as is_alias: true.
For a live look at any Yandex-hosted domain, run it through the free MX lookup and the SPF and DMARC checker.