550 — non-local sender verification failed (Mail.ru)
Retrying will not help. The message will not be delivered.
The reply
550 non-local sender verification failedMail.ru checked whether the domain in your sender address can receive mail, and found nowhere to deliver it. Nothing is wrong with the message — the fix is one DNS record on the sending domain.
What it means
Before accepting a message, Mail.ru verifies the envelope sender: the domain after the @ has to be a place mail can be delivered to, which means it needs an MX record or at least an A record. A subdomain set up only for sending (mail.example.com) usually has neither — just SPF, DKIM and DMARC — so the check fails and the message is refused for good. Perfect authentication does not prevent this: SPF and DKIM say who may send for the domain, this check asks whether the domain exists as a mail destination at all.
Why it happens
- The sending domain is a subdomain with TXT records only — SPF, DKIM, DMARC — and no MX or A record.
- The domain publishes a null MX (MX 0 .), which declares that it accepts no mail.
- The MX record points at a host name that does not resolve.
- A typo in the domain of the From address.
What to do
- Add an MX record for the sending domain itself, not only its parent — for example pointing at the mail server your main domain already uses.
- If there is no mail server to point at, an A record on the sending domain also satisfies the check.
- Wait for the record to propagate, then send a test message to a Mail.ru address.
- If you send through us, the domain's DNS page warns while the sending domain has neither record.
Questions
Does the address need a real mailbox?
Mail.ru does not document the check, but we have seen domains with only an A record pass it, so what matters is that the domain can receive mail. A working mailbox is still the safer setup, and replies to that address need one anyway.
Why does the same message reach Gmail?
Many receivers do not verify the sender this way. Mail.ru does, and it refuses during the SMTP session, so the recipient sees nothing at all.
Will retrying help?
No. The answer stays the same until the record exists. Fix DNS first, then send again.