Temporary SMTP Blocks

MXroute uses automated abuse detection to protect mail servers from traffic that can degrade service for all users. When an IP address triggers one of these rules, SMTP connections from that IP will receive a 554 rejection with a specific error message explaining the cause.

Blocks are temporary and automatically lifted after a timeout period. However, if the abusive behavior continues after a block expires, the IP will be re-blocked and the timeout resets.

Block Rules

Rejected Recipient Flood

• Error message: Your IP is sending excessive rejected recipients. Please contact support.
• Auto-unblock after: 48 hours

Triggered when an IP sends a high volume of messages to recipients that don't exist or are otherwise rejected. Common causes include compromised servers sending spam to harvested address lists, or misconfigured mailing lists with large numbers of stale addresses.

Authentication Failure Flood

• Error message: Your IP is generating excessive authentication failures. Please contact support.
• Auto-unblock after: 24 hours

Triggered when an IP repeatedly fails SMTP authentication. This typically indicates a brute-force password attack or a mail client/application configured with outdated credentials.

Connection Spam

• Error message: Your IP address is flooding our SMTP server with abusive requests, please contact support.
• Auto-unblock after: 12 hours

Triggered when an IP opens an excessive number of connections that get dropped by the server. This usually indicates automated abuse or a misconfigured mail system in a retry loop.

Rejected After DATA

• Error message: Your IP is sending excessive rejected messages. Please contact support.
• Auto-unblock after: 24 hours

Triggered when an IP sends a high volume of messages that are rejected after the message content (DATA phase) is received. This typically indicates spam delivery attempts that are caught by content or policy filters.

What To Do If You Are Blocked

1. Identify the cause. Check the error message to understand which rule was triggered.
2. Fix the underlying issue. Common fixes include:
   • Updating outdated credentials on mail clients or applications
   • Removing invalid recipients from mailing lists
   • Investigating compromised servers or scripts
   • Fixing misconfigured mail systems stuck in retry loops
3. Wait for the block to expire. Blocks are lifted automatically after the timeout period listed above.
4. Contact support if you believe the block was triggered in error or need help identifying the cause.

WARNING

If the underlying issue is not resolved, the IP will be re-blocked automatically once the previous block expires and the problematic traffic resumes.