SFR 450 4.7.1 SFR_IN_103: too many SMTP errors.

The IP generated too many SMTP errors unrelated to other SFR_IN codes.

How to fix 450 4.7.1 SFR_IN_103.

Retrying or final
Retrying
A 4xx reply. Your server keeps the message queued and tries again.
Who is at fault
Sender
Your authentication, reputation, content, or sending pace.
Severity
WarningProtocol Errors
Temporary450 4.7.1 SFR_IN_103

Mismatched TLS, invalid commands, or timeouts lead to SFR_IN_103. The IP is paused for two hours to protect the infrastructure.

Next steps

  1. 1Confirm your HELO/EHLO string is a valid, resolvable hostname.
  2. 2Increase SMTP timeouts so the connection does not drop mid-session.
  3. 3Avoid testing scripts that intentionally send malformed commands.
  4. 4Limit retry attempts during the two-hour suspension window.
SFR documentationEvery raw SMTP 450 reply

The same code at other providers.

Providers word the same code differently. Their fixes differ too.

450 4.7.1 LPN027_503Laposte.netService refusedRetrying

More SFR codes.

Full SFR playbook

Other SFR fixes

421 4.7.0Too many errorsRetrying
450 4.7.1 SFR_IN_101Spam complaintsRetrying
450 4.7.1 SFR_IN_102Virus or malware detectedRetrying
450 4.7.1 SFR_IN_104Unknown usersRetrying
450 4.7.1 SFR_IN_105Volume limit exceededRetrying
450 4.7.1 SFR_IN_106Too many messages per recipientRetrying

In the glossary

Bounce (Soft)A soft bounce is when an email fails to deliver for a temporary reason, like a full inbox or a short outage at the recipient mail server. The address is still valid, and the email may be delivered if you try again later.
DeferralA deferral is when a receiving email server temporarily refuses a message but suggests trying again later.
ThrottlingThrottling is when inbox providers or your email platform slow or limit how many emails you can send in a set time. It acts like a speed limit so big sends do not overwhelm their systems or hurt your reputation.
GreylistingGreylisting is an anti-spam technique where a receiving server temporarily rejects emails from unknown senders to test if they are legitimate.

What SFR expects from senders →

More references.

SMTP field manual.

Every SMTP reply code, with real bounces from mailbox providers and spam filters and who needs to act.

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