SFR SMTP Error Codes
Navigate SFR's complex multi-domain email infrastructure. Understand SFR_IN error codes, reputation-based limits, and 2-hour blocking system.
📡 About SFR Grand Public
Company Overview
- • Founded in 1987, initially mobile telephony
- • Expanded to Internet access and television
- • 2011: Vivendi subsidiary
- • 2014: Acquired by Numericable
- • 2016: Acquired by Altice
- • Single infrastructure for all email domains
Email Infrastructure
- • MX: smtp-in.sfr.fr for all domains
- • Covers 20+ email domains
- • Unified filtering policy
- • Uses market anti-spam solutions
- • Partners with Signal Spam for FBL
🌐 SFR Email Domains
All these domains use the same infrastructure. SFR Grand Public applies the same filtering policy to all of its email services:
🔍 Understanding SFR_IN Error Codes
SFR uses a unique error code system: SFR_IN_XXX
Code Structure:
- SFR_IN_ - SFR Grand Public code for inbound connection
- First digit - Internal information to SFR Grand Public
- Last two digits - Specific error type:
Each code has its own trigger threshold based on a specific observation period
SFR SMTP Error Codes Explained
421 4.7.0
Error: too many errors
Your connection has generated too many SMTP errors. SFR has temporarily blocked further communication. Example: "421 4.7.0 msfrf2604.sfr.fr Error: too many errors"
How to Fix:
- ✓Review your SMTP implementation for protocol compliance
- ✓Fix any authentication or formatting issues
- ✓Wait for the 2-hour block to expire before retrying
- ✓Monitor error rates to stay below thresholds
450 4.7.1
SFR_IN_101Service refused due to bad behavior - Too many spam messages
Your IP has been blocked for sending too many messages classified as spam. This triggers a 2-hour block.
How to Fix:
- ✓Review email content for spam triggers
- ✓Verify list quality and permission
- ✓Check spam complaint rates via Signal Spam FBL
- ✓Improve content quality and engagement
450 4.7.1
SFR_IN_102Service refused due to bad behavior - Virus detected
Messages from your IP contained viruses or malicious content. This results in an immediate 2-hour block.
How to Fix:
- ✓Scan your systems for malware immediately
- ✓Check for compromised accounts
- ✓Review all attachments and links
- ✓Implement outbound virus scanning
450 4.7.1
SFR_IN_103Service refused due to bad behavior - Too many SMTP errors
Excessive SMTP protocol errors (not related to other SFR_IN codes). Your IP is blocked for 2 hours.
How to Fix:
- ✓Fix SMTP protocol compliance issues
- ✓Ensure proper command syntax
- ✓Check for connection timeout issues
- ✓Review MTA configuration
450 4.7.1
SFR_IN_104Service refused due to bad behavior - Too many unknown users
Your IP has hit too many non-existent recipients. This indicates poor list quality and triggers a 2-hour block.
How to Fix:
- ✓Clean your mailing list immediately
- ✓Remove all invalid addresses
- ✓Implement email validation before sending
- ✓Use double opt-in for new subscribers
450 4.7.1
SFR_IN_105Service refused due to bad behavior - Too many messages sent
You've exceeded the allowed message volume for your reputation level. IP blocked for 2 hours.
How to Fix:
- ✓Reduce sending volume to match reputation
- ✓Build reputation gradually over time
- ✓Monitor connection limits based on reputation
- ✓Implement proper rate limiting
550 5.1.1
Recipient address rejected: User unknown
The recipient email address does not exist at SFR. This is a permanent failure.
How to Fix:
- ✓Remove this address from your list immediately
- ✓Do not retry sending to this address
- ✓Implement proper bounce handling
- ✓Track and suppress hard bounces
552 5.2.2
Mailbox over quota
The recipient's mailbox has exceeded its storage limit and cannot accept new messages.
How to Fix:
- ✓Treat as a soft bounce
- ✓Retry over several days
- ✓Suppress after 3-5 consecutive failures
- ✓Monitor for patterns indicating abandoned accounts
550 5.7.1
Email rejected per SPAM policy
Your message has been rejected due to content or reputation issues triggering SFR's spam policy.
How to Fix:
- ✓Review email content and structure
- ✓Check sender reputation and authentication
- ✓Avoid spam trigger words and phrases
- ✓Ensure proper list permission and engagement
SFR Best Practices
Reputation Management
- •Connection limits based on reputation
- •Messages per connection varies by reputation
- •Hourly connection limits by reputation
- •Build reputation gradually over time
Authentication
- •SPF authentication recommended
- •DKIM signing recommended
- •Use consistent sending domains
- •Avoid shared infrastructure if possible
Error Code System
- •SFR_IN prefix for inbound connections
- •Last two digits indicate error type
- •All blocks last exactly 2 hours
- •Each code has specific thresholds
List Quality
- •Monitor invalid recipient rates (SFR_IN_104)
- •Track spam classifications (SFR_IN_101)
- •Access FBL via Signal Spam
- •Clean lists regularly to avoid blocks
Technical Configuration
SFR Connection Settings
MX: smtp-in.sfr.fr
concurrent_connections_per_IP = based_on_reputation
messages_per_connection = based_on_reputation
connections_per_IP_per_hour = based_on_reputation
SPF: Recommended
DKIM: Recommended
Complaint Feedback Loops
📈 Aggregated FBL
CSV format with daily complaint volumes by IP:
- • Available to Signal Spam members only
- • Daily aggregated data
- • IP-based complaint tracking
📧 ARF Feedback Loop
Individual complaint reports in ARF format:
- • Signal Spam members
- • Validity FBL ($18+ per year)
- • Real-time complaint notifications
Note: Some monitoring tools like Postmastery integrate data from the aggregated FBL through their partnership with Signal Spam, making it easier to track SFR complaint rates.
⏱️ Important: 2-Hour Blocking System
Block Duration
- • All SFR_IN blocks last exactly 2 hours
- • No early removal possible
- • Blocks apply per sending IP
- • Multiple blocks can overlap
Prevention Strategy
- • Monitor error rates closely
- • Stay below trigger thresholds
- • Use multiple IPs for large volumes
- • Implement circuit breakers
📞 Contacting SFR Support
Contact SFR's abuse handling unit at: [email protected]
Include the following information:
- ✓Date and time of occurrence
- ✓Sending IP address(es)
- ✓Sending hostname(s)
- ✓Sending domain
- ✓Complete SMTP error with SFR_IN code
Struggling with SFR Delivery?
SFR's multi-domain infrastructure and 2-hour blocking system require careful management. Let us help you navigate their reputation-based limits and avoid costly blocks.