How to solve or interpret following error? I'm not sure if anything should be done on client (sender or sending account of a domain) or ask remote postmasters for help.

<[email protected]> (expanded from <[email protected]>): host
    smtpz4.laposte.net[] said: 521 5.7.1 Service unavailable;
    client blocked using Return-Path. Les emails envoyes vers la
    messagerie Laposte.net ont ete bloques par nos services. Afin de
    regulariser votre situation, nous vous invitons a cliquer sur le lien
    ci-dessous et a suivre la procedure. The emails sent to the mail host
    Laposte.net were blocked by our services. To regularize your situation
    please click on the link below and follow the procedure
    https://senderscore.org/rtbl/. LPN007_102 (in reply to RCPT TO command)
  • IIUC, the mail server (client forwarding the mail to final destination at smtpz4.laposte.net does not have Sender Rewriting Scheme implemented (SRS) or misconfigured. This causes smtpz4.laposte.net reject the mail as original sender domain has SPF policy which does not permit forwarding mail server to re-send the mail with original domain included in 'Return-Path'. Am I right?
    – Jiri B
    Jan 5, 2021 at 11:36
  • You could start by clicking the link. Jan 6, 2021 at 1:49
  • Vague "political" message which doesn't explain anything in technical way.
    – Jiri B
    Jan 6, 2021 at 9:08
  • And yet it is what you need to do. Jan 6, 2021 at 10:03


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