Zoho

5.4.1

Zoho relayed a rejection from the destination domain's filters. Contact that domain's admin through another channel to allow delivery.

1

Zoho blocked delivery under the recipient domain's policy. Contact that domain's admin to adjust filters if the mail is legitimate.

4.3.1

Zoho is not accepting mail for this domain right now. Retry with backoff.

5.7.1

Zoho rejected this under DMARC for a zoho.com From address. Send through Zoho SMTP settings, or stop using that From on an external ESP.

5.1.1

Zoho says this mailbox does not exist. Treat it as a hard bounce and remove the address.

5.1.1

Zoho blocked delivery under a mailbox policy error. Contact the recipient admin if the address should accept mail.

5.7.1

Zoho detected a virus in the message. Scan content, attachments, and URLs, remove the threat, then resend.

5.1.1

Zoho disallowed relaying for this destination. Authenticate properly and send only to accepted Zoho recipients.

5.2.3

Zoho blocked delivery for a mail policy violation. Check Zoho community docs for the policy details, then adjust content or routing.

5.7.1

Zoho flagged the email as spam. Clean content and authentication, then retry only if the send is legitimate.