Bounce Labels Reference
Use these labels when submitting proposals or uploading CSV files.
The label column in your CSV must contain one of the values below (case-insensitive).
| Label | Description | Example SMTP Response |
|---|---|---|
auth_failure |
Authentication or validation failure. The sending domain failed SPF, DKIM, or DMARC checks. | 550 5.7.1 Unauthenticated email is not accepted due to domain DMARC policy. |
domain_blacklisted |
The sender's domain has been blacklisted by the recipient server or a DNS-based blocklist. | 550 5.7.1 Rejected - domain example.com is listed on Spamhaus DBL. |
geo_blocked |
The message was blocked due to geographic origin restrictions on the sender's IP or region. | 550 5.7.1 Mail from your region is not allowed. |
greylisting |
Temporary deferral asking the sender to retry later. The server uses greylisting to reduce spam. | 421 4.7.0 Try again later, closing connection. |
invalid_address |
The email address is malformed or syntactically invalid (not the same as a non-existent user). | 553 5.1.3 Invalid address format. |
ip_blacklisted |
The sender's IP address is on a blocklist (e.g., Spamhaus ZEN, Barracuda, Sorbs). | 550 5.7.1 Service unavailable, IP blocked by Spamhaus ZEN. |
mailbox_disabled |
The recipient's mailbox exists but has been disabled, suspended, or deactivated. | 550 5.2.1 The email account has been suspended. |
mailbox_full |
The recipient's mailbox has exceeded its storage quota and cannot accept new messages. | 552 5.2.2 The email account that you tried to reach is over quota. |
policy_blocked |
The recipient server rejected the message due to a local policy (content filter, attachment policy, etc.). | 550 5.7.1 Message rejected per organizational policy. |
rate_limited |
Too many connections or messages from the sender in a short time. Typically a temporary condition. | 421 4.7.28 Too many connections from your IP address. Try again in 30 minutes. |
relay_denied |
The server does not relay mail for the specified domain. Usually a misconfiguration or open relay check. | 550 5.7.1 Unable to relay. |
server_error |
A temporary internal error on the recipient mail server (e.g., disk full, service crash). | 451 4.3.0 Mail server temporarily unavailable. Please try again later. |
spam_blocked |
The message was rejected because it was classified as spam by the recipient server's content filter. | 550 5.7.1 Message rejected due to content restrictions (spam). |
unknown |
The bounce reason could not be determined from the SMTP response. Use this when no other label fits. | 550 Requested action not taken. |
user_unknown |
The recipient email address does not exist on the server. The most common permanent bounce. | 550 5.1.1 The email account that you tried to reach does not exist. |
virus_detected |
The message was rejected because it contains a virus, malware, or a prohibited attachment type. | 552 5.7.0 Our system detected an illegal attachment on your message. |