General questions about Yandex Cloud Postbox
Is there support for Cyrillic domains?
Yes, Yandex Cloud Postbox supports Cyrillic domains (IDN). To use a Cyrillic domain, specify it in Punycode encoding when creating an address. For example, the domain пример.рф will appear as xn--e1afmkfd.xn--p1ai in Punycode.
Can I use my Yandex 360 organization's primary domain for Yandex Cloud Postbox mailings?
Yes, you can specify your Yandex 360 organization's domain in the address settings and send your emails from it.
Are there any Yandex 360 or Yandex Cloud Postbox quotas and limits when using a Yandex 360 domain?
Yandex Cloud Postbox quotas and limits apply when using any domains. For more information, see Yandex Cloud Postbox quotas and limits.
Is it required to create an SPF record?
No, creating an SPF record on your custom domain is not required. Each email sent via Yandex Cloud Postbox is signed with two DKIM signatures: one from postbox.yandexcloud.net, our technical domain (with its SPF record preconfigured), and a second from your custom domain. In most cases, such authentication is sufficient for successful email delivery.
However, if the recipient has strict incoming mail screening policies, you may need to add an SPF record to your custom domain as well. Learn how to do this in SPF.
Why do I need to add two CNAME records when setting up Easy DKIM, but the TXT record resolves only through one of them?
Two CNAME records are required to enable Yandex Cloud Postbox to automatically rotate DKIM key pairs. Public key TXT records resolve through both CNAME records only during key rotation. At other times, only a single TXT record is available. For more information, see DKIM key rotation.
Why is email delivery delayed?
One common cause of delays is greylisting (greylisting) on the recipient's mail server. This is an anti-spam technique where the server temporarily rejects the first email delivery attempt assuming that a legitimate mail server will repeat it later.
Yandex Cloud Postbox will automatically retry delivery. Usually, after the delay set by the recipient's server, the email will be accepted and delivered.
Why was an email not sent to the recipient?
One possible reason is that the recipient's address is on a suppression list. For more information, see Suppression lists.
Why does my connection drop with a 421 4.4.2 Idle timeouterror?
The SMTP connection remains open for as long as the client is sending commands: the idle timeout restarts on each command received by the server. If the pause between commands exceeds the allowed idle time (around one minute), the server will respond with 421 4.4.2 Idle timeout, bye bye and close the connection. This error comes between transactions, so the email is neither lost nor duplicated. To continue sending, establish a new connection.
To avoid getting this error:
- If using a connection pool, send emails in succession, send the
NOOPcommand more often than once per minute (any command resets the idle timeout), or close the connection with theQUITcommand and open a new one before the next send. - Your pauses between retries, including after the
454 Maximum sending rate exceedederror, should be between connections, not during an active connection. - The message body must fit entirely within the same timeout after the
DATAcommand; the timeout is counted from theDATAcommand. Otherwise, the server will return the451 4.4.2 Timeout waiting for data from clienterror. If your data transmission channel is slow and the attachments are large, reduce the size of the email.
The 421 4.4.2 error is neither a quota error nor a bounce. For more on SMTP responses, see SMTP responses.