Sender or sending IP blocked
The receiving server does not allow this sender or sending IP.
What to do now
- Read the complete reply for the blocking reason.
- Check the actual sending IP and domain state.
- If needed, ask the receiving administrator why it is blocked and how to resolve it.
Representative reply
550 Sender on the blocklist
Retry decision
Resend after confirming the block is removed.
Why it happens
A receiving blocklist or sender reputation policy may apply.
Typical stage
MAIL FROM
- CONNECT
- EHLO
- MAIL FROM
- RCPT TO
- DATA
- DELIVERY
Stages vary by server. Confirm the actual stage from the complete reply and session logs.
What is SMTP Reply Code?Open only the explanations you need
Three-digit server reply: 4xx is transient, 5xx permanent. Read the complete text to investigate the cause.
What is Enhanced Status Code?Open only the explanations you need
An extended status such as 5.1.1. Server wording and usage may vary.
Check directly
- Read the complete reply for the blocking reason.
- Check the actual sending IP and domain state.
- If needed, ask the receiving administrator why it is blocked and how to resolve it.
If you operate or diagnose the mail server, the tools below can help with these checks.
Cautions
Observed DSNs do not map one-to-one to causes. The stage shown is typical; confirm it with the full reply and actual logs.
Similar reply wording and observed status codes
sender is in my black liston the blockliston the block listregistered as spammer
Observed DSNs: Message first