Laposte.net 450 4.7.1 LPN027_503: service refused.

Laposte temporarily refused the connection after seeing too many errors or complaints.

How to fix 450 4.7.1 LPN027_503.

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
WarningService Refused
Temporary450 4.7.1 LPN027_503

LPN027_503 is Laposte’s generic throttle when reputation drops. It normally clears after a few hours if you slow delivery and clean your list.

Next steps

  1. 1Reduce concurrent SMTP connections to no more than two per IP.
  2. 2Respect Laposte’s limit of ~100 messages per connection.
  3. 3Pause unengaged French recipients and remove obvious spam traps.
  4. 4Check the Signal Spam feedback loop for complaint spikes.
Laposte.net 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 SFR_IN_101SFRSpam complaintsRetrying
450 4.7.1 SFR_IN_102SFRVirus or malware detectedRetrying
450 4.7.1 SFR_IN_103SFRToo many SMTP errorsRetrying
450 4.7.1 SFR_IN_104SFRUnknown usersRetrying
450 4.7.1 SFR_IN_105SFRVolume limit exceededRetrying
450 4.7.1 SFR_IN_106SFRToo many messages per recipientRetrying
450 4.7.1 SFR_IN_107SFRInvalid HELO or reverse DNSRetrying

More Laposte.net codes.

Full Laposte.net playbook

Other Laposte.net fixes

450 4.1.8 LPN007_405Invalid senderRetrying
450 4.1.7 LPN007_411MX misconfigurationRetrying
450 4.2.1Mailbox inactiveRetrying
450 4.7.0 LPN007_510Service refusedRetrying
451 4.7.1 LPN007_512Spam suspicionRetrying
550 5.1.1 LPN007_416Invalid recipientFinal

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 Laposte.net expects from senders →

More references.

SMTP field manual.

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